Download Geometry (G) Draw, construct, and describe geometrical figures and

Geometry (G)
Draw, construct, and describe geometrical figures and describe the relationships between them.
Standard: CC.7.G.1 Solve problems involving scale drawings of geometric figures, including computing actual lengths and areas from a scale
drawing and reproducing a scale drawing at a different scale.
The intent of this standard is… Students determine the dimensions of figures when given a scale and identify the impact of a scale on actual length
(one-dimension) and area (two-dimensions). Students identify the scale factor given two figures. Using a given scale drawing, students reproduce the
drawing at a different scale. Students understand that the lengths will change by a factor equal to the product of the magnitude of the two size
transformations.
Learning Targets




create a scale
drawing using a
different scale.
calculate the
missing length in a
scale drawing using
proportional
reasoning.
calculate the area
of a scale drawing
using proportional
reasoning.
describe the
relationship
between two given
figures.
Notes for teacher


This standard has a
natural tie to 7.RP.A.1
– calculating unit rates
Connects to 8th grade
8.G.3 and 8.G.4
Samples

Julie shows the scale drawing of her room below. If each 2 cm on the
scale drawing equals 5 ft, what are the actual dimensions of Julie’s
room? Reproduce the drawing at 3 times its current size.
Solution:
Common
misconceptions

Students may have
difficulty correctly
setting up
proportions.
5.6 cm 14 ft
1.2 cm3 ft
2.8 cm7 ft
4.4 cm11 ft
4 cm10 ft

If the rectangle below is enlarged
using a scale factor of 1.5, what will be the perimeter and area of the
new rectangle?
7 in.
2 in.
Solution:
The perimeter is linear or one-dimensional. Multiply the perimeter of the
given rectangle (18 in.) by the scale factor (1.5) to give an answer of 27
Madison County Schools
Spring 2014
in. Students could also increase the length and width by the scale factor
of 1.5 to get 10.5 in. for the length and 3 in. for the width. The perimeter
could be found by adding 10.5 + 10.5 + 3 + 3 to get 27 in.
The area is two-dimensional so the scale factor must be squared. The
area of the new rectangle would be 14 x 1.52 or 31.5 in2.

Triangle ADE is proportional to Triangle ABC. The length of DE is
20 ft.; the length of AB is 6ft. and the length of
BC is 8 ft. What is
the length of AD ?
A
Solution:
One possible solution is to recognize that because
the triangles are proportional, the side lengths must
B
6
x
=
could
8 20
D
be in the same ratio. The proportion
C
E
be used to calculate that the length of AD is 15 ft.
Other proportions and reasoning about the relationships between the
triangles are possible.
Vocabulary
fraction, ratio, scale, scale drawing, scale factor, unit
rate
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Mathematical Practices
1 - Make sense of problems and persevere in solving them.
2 - Reason abstractly and quantitatively.
3 - Construct viable arguments and critique the reasoning of others.
4 - Model with mathematics.
5 - Use appropriate tools strategically.
6 - Attend to precision.
7 - Look for and make use of structure.
8 - Look for and express regularity in repeated reasoning.
Spring 2014
Resources
Madison County Schools
Spring 2014
Geometry (G)
Draw, construct, and describe geometrical figures and describe the relationships between them.
Standard: CC.7.G.2 Draw (freehand, with ruler and protractor, and with technology) geometric shapes with given conditions. Focus on constructing
triangles from three measures of angles or sides, noticing when the conditions determine a unique triangle, more than one triangle, or no triangle.
The intent of this standard is… Students draw geometric shapes with given parameters. Parameters could include parallel lines, angles,
perpendicular lines, line segments, etc.
Learning Targets



construct triangles
from three given
angle measures
resulting in unique
triangles by drawing
free-hand or using
rulers, protractors,
or technology.
construct triangles
from three given
angle measures
resulting in more
than one triangle by
drawing free-hand
or using rulers,
protractors, or
technology.
construct triangles
from three given
angle measures
resulting in no
triangles by drawing
free- hand or using
rulers, protractors,
or technology.
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Notes for teacher


Allowing students to
try creating triangles
with given side and/or
angle measures
before sharing the
rules with them
enables them to
discover the rules on
their own.
The Pythagorean
Theorem is not
expected here.
Samples

Will three sides of any length create a triangle? Explain how you
know which will work. Possibilities to examine are:
1. 13 cm, 5 cm, and 6 cm
2. 3 cm, 3cm, and 3 cm
3. 2 cm, 7 cm, 6 cm
Solution:
Common
misconceptions


“A” above will not work; “B” and “C” will work. Students recognize that
the sum of the two smaller sides must be larger than the third side.

Is it possible to draw a triangle with a 90 ̊ angle and one leg that is 4
inches long and one leg that is 3 inches long? If so, draw one. Is
there more than one such triangle?
(NOTE: Pythagorean Theorem is NOT expected – this is an
exploration activity only)

Draw a triangle with angles that are 60 degrees. Is this a unique
triangle? Why or why not?

Draw an isosceles triangle with only one 80°angle. Is this the only
possibility or can another triangle be drawn that will meet these
conditions?

Students may
believe that the rule
for the side lengths
is the same as the
rule for the angle
measures.
Students may not
realize that
measurements
need to be exact.
Such as, if it says a
side is 8cm it
cannot be 8.1cm.
If drawing free
hand students may
have difficulty using
a ruler/protractor.
Spring 2014
Vocabulary
acute triangle, equilateral triangle, isosceles triangle,
right triangle, obtuse triangle, scalene triangle
Mathematical Practices
4 - Model with mathematics.
5 - Use appropriate tools strategically.
6 -Attend to precision.
7 - Look for and make use of structure.
8 - Look for and express regularity in repeated reasoning.
Resources
Madison County Schools
Spring 2014
Geometry (G)
Draw, construct, and describe geometrical figures and describe the relationships between them.
Standard: CC.7.G.3
Describe the two-dimensional figures that result from slicing three-dimensional figures, as in plane sections of
right rectangular prisms and right rectangular pyramids.
The intent of this standard is… Students need to describe the resulting face shape from cuts made parallel and perpendicular to the bases of right
rectangular prisms and pyramids. Cuts made parallel will take the shape of the base; cuts made perpendicular will take the shape of the lateral (side) face.
Cuts made at an angle through the right rectangular prism will produce a parallelogram
Learning Targets
Notes for teacher
Samples
Common
misconceptions

describe the twodimensional figures
that result from
slicing a 3-D figure.
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
Look for concrete
models. Students
have a difficult time
visualizing cuts
through a plane.

Using a clay model of a rectangular prism, describe the shapes that
are created when planar cuts are made diagonally, perpendicularly,
and parallel to the base.

If the pyramid is cut with a plane (green) parallel to the base, the
intersection of the pyramid and the plane is a square cross section
(red).

If the pyramid is cut with a plane (green) passing
through the top vertex and perpendicular to the base,
the intersection of the pyramid and the plane is a
triangular cross section (red).

If the pyramid is cut with a plane (green) perpendicular
to the base, but not through the top vertex, the
intersection of the pyramid and the plane is a trapezoidal
cross section (red).

Students will
misinterpret aerial
and lateral views.
Spring 2014
Vocabulary
lateral, parallel, perpendicular, plane, prism, pyramid
Mathematical Practices
2 - Reason abstractly and quantitatively.
4 - Model with mathematics.
5 - Use appropriate tools strategically.
7 - Look for and make use of structure.
Resources
Madison County Schools
Spring 2014
Geometry (G)
Draw, construct, and describe geometrical figures and describe the relationships between them.
Standard: CC.7.G.4
Know the formulas for the area and circumference of a circle and use them to solve problems; give an informal derivation of
the relationship between the circumference and area of a circle.
The intent of this standard is… Students understand the relationship between radius and diameter. Students also understand the ratio of
circumference to diameter can be expressed as pi. Building on these understandings, students generate the formulas for circumference and area.
Learning Targets
Notes for teacher
Samples
Common
misconceptions





apply the formula
for area of a circle
to solve problems.
apply the formula
for circumference to
solve problems.
find the area of a
circle given the
circumference.
find the
circumference of a
circle given the
area.
describe and justify
the relationship
between area and
circumference of a
circle.


The illustration shows the
relationship between the
circumference and area. If
a circle is cut into wedges
and laid out as shown, a
parallelogram results. Half
of an end wedge can be
moved to the other end a
rectangle results. The
height of the rectangle is
the same as the radius of
the circle. The base length
is
1
the circumference
2

The seventh grade class is building a mini-golf game for the
school carnival. The end of the putting green will be a circle. If
the circle is 10 feet in diameter, how many square feet of grass
carpet will they need to buy to cover the circle? How might
someone communicate this information to the salesperson to
make sure he receives a piece of carpet that is the correct size?
Use 3.14 for pi.

Solution:
Area = ∏r2
Area = 3.14 (5)2
Area = 78.5 ft2
To communicate this information, ask for a 9 ft by 9 ft
square of carpet.
(2∏r). The area of the
rectangle (and therefore the
circle) is found by the
following calculations:
Area Rectangle = Base x
Height
Area = ½ (2∏r) x r
Madison County Schools

Students may
believe Pi is an
exact number
rather than
understanding that
3.14 is just an
approximation of
pi.
Many students are
confused when
dealing with
circumference
(linear
measurement) and
area. This
confusion is about
an attribute that is
measured using
linear units
(surrounding) vs.
an attribute that is
measured using
area units
(covering).
Cont…
Spring 2014

The center of the circle is at (2, -3). What is the area of the
circle?
Area = ∏r x r
Area = ∏r2
http://mathworld.wolfram.com/C
ircle.html

“Know the formula” does
not mean memorization of
the formula. To “know”
means to have an
understanding of why the
formula works and how the
formula relates to the
measure (area and
circumference) and the
figure. This understanding
should be for all students.
Solution:
The radius of the circle of 3 units. Using the formula, Area =
∏r2, the area of the circle is approximately 28.26 units2.
Students build on their understanding of area from 6th grade
to find the area of left-over materials when circles are cut
from squares and triangles or when squares and triangles
are cut from circles.
Cont…
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Spring 2014

What is the
perimeter of the
inside of the
track.
Solution:
The ends of the track are two semicircles, which
would form one circle with a diameter of 62m. The
circumference of this part would be 194.68 m. Add
this to the two lengths of the rectangle and the
perimeter is 394.68m
Vocabulary
Circumference, diameter, Pi, radius
Madison County Schools
Mathematical Practices
1 - Make sense of problems and persevere in solving them.
2 - Reason abstractly and quantitatively.
3 - Construct viable arguments and critique the reasoning of others.
4 - Model with mathematics.
5 - Use appropriate tools strategically.
6 - Attend to precision.
7 - Look for and make use of structure.
8 - Look for and express regularity in repeated reasoning.
Resources
Spring 2014
Geometry (G)
Draw, construct, and describe geometrical figures and describe the relationships between them.
Standard: CC.7.G.5
Use facts about supplementary, complementary, vertical, and adjacent angles in a multi-step problem to write and solve
simple equations for an unknown angle in a figure.
The intent of this standard is… Students should understand special relationships between angles and use those relations to write and solve
equations to find the measures of unknown angles.
Learning Targets
Notes for teacher
Samples
Common
misconceptions



identify and
recognize types of
angles:
supplementary,
complementary,
vertical, adjacent.
calculate the
complement and
supplement of a
given angle.
determine an
unknown angle
measure by writing
and solving
equations based
upon relationships
among angles.


Relationships of angles on
a transversal must be
understood.
For 7.G.B.5, instruction
should ensure that students
have opportunities to solve
multi-step problems.

Write and solve an equation to find the measure of angle x.


Solution:
Students may have
difficulty identifying
the alternate
interior and exterior
angels.
Students must
identify vertical
angles and
understand that
they are congruent.
The measure of angle x is supplementary to 50°, so subtract
50 from 180 to get a measure of 130° for x.

Find the measure of angle x.
Solution:
First, find the missing angle measure of the bottom triangle
(180 – 30 – 30 = 120). Since the 120 is a vertical angle to x,
the measure of x is also 120°.
Madison County Schools
Spring 2014

Find the measure of angle b.
Note: Not drawn to scale.
Solution:
Because, the 45°, 50° angles and b form are supplementary
angles, the measure of angle b would be 85°. The
measures of the angles of a triangle equal 180° so 75° +
85°+ a = 180°. The measure of angle a would be 20°.
Vocabulary
adjacent angles, complimentary angles, supplementary
angles, transversal, vertical angles
Madison County Schools
Mathematical Practices
3 - Construct viable arguments and critique the reasoning of others.
4 - Model with mathematics.
5 - Use appropriate tools strategically.
6 - Attend to precision.
7 - Look for and make use of structure.
Resources
Spring 2014
Geometry (G)
Draw, construct, and describe geometrical figures and describe the relationships between them.
Standard: CC.7.G.6
Solve real-world and mathematical problems involving area, volume and surface area of two- and three-dimensional objects
composed of triangles, quadrilaterals, polygons, cubes, and right prisms.
The intent of this standard is… to apply geometric formulas to calculate area, volume, and surface area of figures; and to understand that surface
area is finding the area of a net of a 3D figure made up of several smaller geometric figures.
Learning Targets
Notes for teacher
Samples
Common
misconceptions




find the area of
triangles,
quadrilaterals, and
polygons.
find the surface
area of cubes and
right prisms.
solve real world and
mathematical
problems involving
area, surface area
and volume.
find volume of
cubes and right
prisms.





instruction should ensure
that students have
opportunities to solve multistep problems.
solving multi-step problems
coherently reinforces
instruction around 7.EE.B.3
and 7.EE.B.4a.
Students understanding of
volume can be supported
by focusing on the area of
base times the height to
calculate volume. Students
understanding of surface
area can be supported by
focusing on the sum of the
area of the faces. Nets can
be used to evaluate surface
area calculations.
Students are taught the
area formulas in 6th grade,
with application being
taught in 7th.
Connects to 8th grade 8.G.9

Choose one of the figures shown below and write a step by step
procedure for determining the area. Find another person that
chose the same figure as you did. How are your procedures the
same and different? Do they yield the same result?



A cereal box is a rectangular prism. What is the volume of the
cereal box? What is the surface area of the cereal box? (Hint:
Create a net of the cereal box and use the net to calculate the
surface area.) Make a poster explaining your work to share with
the class.

Find the area of a triangle with a base length of three units and a
height of four units.

Find the area of the trapezoid shown below using the formulas
for rectangles and triangles.
Students can have
a difficult time
choosing the
appropriate
formula.
Students can also
have a difficult time
sub-dividing figures
on their own,
especially when
there are multiple
ways to make the
splits. Use of
exemplars can be
helpful when
demonstrating this
skill.
12
3
7
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Spring 2014
Vocabulary
adjacent, area, circumference, complementary, diameter,
plane section, polygon, prism, pyramid, quadrilateral,
supplementary, surface area, triangle, vertical, volume
Madison County Schools
Mathematical Practices
1 - Make sense of problems and persevere in solving them.
2 - Reason abstractly and quantitatively.
3 - Construct viable arguments and critique the reasoning of others.
4 - Model with mathematics.
5 - Use appropriate tools strategically.
6 - Attend to precision.
7 - Look for and make use of structure.
8 - Look for and express regularity in repeated reasoning.
Resources
Spring 2014