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Geometry Notes
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Terms we need to know for Geometry
a. Plane Figures- A flat 2 dimensional figure
i. Example: Show examples
b. Congruent- means equal in length or degree
i. Examples drawings. Also show the symbols for congruencies.
c. Parallel- two or more lines on the same plane that never touch.
i. Show the symbol for parallel.
d. Right angle- A 90 degree angle.
i. Show symbol for right angle.
e. Regular Figure- Any plane figure that all sides are congruent and all
angles are congruent.
i. Example: Show example
Angles- Angles are measured in degrees.
a. Right Angle- A 90 degree angle
b. Obtuse angle- An angle greater than 90 degrees
c. Acute angle- An angle less that 90 degrees
Polygons- to be a polygon a figure must have the following traits:
a. Have at least three sides
b. All sides are straight
c. The figure must be closed.
d. All polygons are named by the number of sides they have.
i. Triangle- A three sided polygon
ii. Quadrilateral- A four sided polygon
iii. Pentagon- a five sided polygon.
iv. Hexagon- A six sided Polygon
v. Octagon- An eight sided Polygon
vi. Decagon- A ten sided Polygon.
Triangles- We identify triangles two ways.
a. We identify triangles by number of congruent sides.
i. Equilateral triangle- All sides of the triangle are Congruent.
ii. Isosceles Triangle- Two sides of the triangle are equal.
iii. Scalene triangle- No sides of a triangle are congruent.
b. We identify triangles by there interior angles. Interior means angles inside
the triangle.
i. Right triangle- One of the three angles is a right angle.
ii. Acute Triangle- all three angles in the triangle are less than 90
degrees.
iii. Obtuse Triangle- One of the angles is greater than 90 degrees.
c. We can put both together to get the following types of triangles.
i. Right Scalene Triangle- Has a right angle and no sides are
congruent
ii. Right Isosceles triangle- A right angle and two sides are congruent.
iii. Can we have a Right Equilateral triangle?- NO
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iv. Obtuse Scalene Triangle- One angle greater than 90 degrees and
sides are congruent.
v. Obtuse Isosceles triangle- One angle greater than 90 degrees and
no sides are congruent.
vi. Can we have an Obtuse Equilateral triangle- NO
vii. Acute Equilateral triangle- all angles are equal and all sides are
congruent.
viii. Can we have an Acute Scalene triangle- Yes
ix. Can we have an Acute Isosceles Triangle – Yes
d. Important fact about Triangles to make the above easier to remember.i. If two angles are congruent the sides opposite them must be
congruent.
Quadrilaterals- Any 4 sided polygon
a. Types of Quadrilateralsi. A trapezoid1. One pair of opposite sides has to be parallel.
ii. A Parallelogram1. Opposite sides are Parallel
2. Opposite angles are congruent
iii. A Rhombus1. Opposite sides are Parallel
2. Opposite angles are congruent
3. All sides are congruent.
iv. A Rectangle1. Opposite sides are Parallel
2. All angles are 90 degrees
v. A Square1. Opposite sides are Parallel
2. All angles are 90 degrees
3. All sides are congruent