Download Lesson 7-7a

7-7
6th grade math
Triangles
Objective
• To classify and draw triangles, and find missing
angles in triangles.
• Why? To further your knowledge in
measurement and geometry and keeping
building a strong foundation in MG in HS
California State Standards
MG 2.3: Draw … triangles from information about
them (e.g., … a right isosceles triangle).
AF 1.1 : Write and solve one-step equations in one
variable.
AF 3.2: Express in symbolic form simple relationships
arising from geometry
MG 2.0: Identify and describe the properties of twodimensional figures.
MR 2.4: Use a variety of methods, such as words,
numbers, symbols, charts, graphs, tables, diagrams,
and models, to explain mathematical reasoning.
Vocabulary
• Triangles
– 3 sided figure and the sum of the angles are 180°.
Remember that a triangle is ½ a square or rectangle
(whose angles measure 360°).
• Congruent triangles
– Triangles with the same size and shape
• Equilateral triangle
Vocabulary
– A triangle with all three sides congruent
• Scalene triangle
– A triangle with no sides congruent (all 3 sides are
different)
• Isosceles triangle
– A triangle with 2 sides congruent sides
• Right triangle
– A triangle with a right angle (only 1 angle is needed)
• Acute triangle
Vocabulary
– A triangle with all three angles with acute
measures
• Obtuse triangle
– A triangle with an obtuse angle (only 1 angle is
needed) ↓
Classifying Triangles
Classified by Sides
*Three congruent sides
- equilateral triangle
*Two congruent sides
- isosceles triangle
- may be acute, right, or
obtuse
*No congruent sides
- scalene triangle
-may be acute, right, or
obtuse
Classified by Angles
*All acute angles
- acute triangle
- may be equilateral,
isosceles, or scalene
*One right angle
- right triangle
- may be isosceles or
scalene
*One obtuse angle
- obtuse triangle
-may be isosceles or
scalene
How to Find Missing Angles of a
Triangle
1) Add the 2 known angles
2) Subtract 180 from Step 1
3) Check work
Triangle with known sides
90° and 30°.
90°+ 30° = 120°
180° – 120° = 60°
3rd side = 60°
Try It!
Classify each triangle in 2 ways
1.
1) Scalene, right
2.
2) Isosceles, acute
3) Scalene, obtuse
3.
4.
4) Equilateral, acute
Try Some More!
Find the m∠ of the third angle of
teach triangle
5) ∠’s: 98°, 40°, ___
5) 180 – (98 + 40)
= 42°
6) ∠’s: 29°, 84°, ___
6) 180 – (29 + 84)
= 67°
Scalene, obtuse
Scalene, acute
7) ∠’s: 72°, 46°, ___
8) ∠’s: 43°, 25°, ___
7) 180 – (72 + 46)
= 62°
Scalene, acute
8) 180 – (43 + 25)
= 112°
Scalene, obtuse
Objective Review
• To classify and draw
triangles, and find missing
angles in triangles.
• Why? You have furthered your
knowledge in measurement and
geometry and keeping building a
strong foundation in MG in HS
• You can classify and draw triangles
according to side and angle measures.
By knowing that the sum of the
angles of a triangle is 180°, you can
find the measure of an unknown
angle.
Independent Practice
• Complete problems 1023
• Copy original problem
first.
• Show all work!
• If time, complete Mixed
Review: 24-30
• If still more time, work
on Accelerated Math.