Download Geometry Missing Angles Somethings you need to know about

Geometry
Missing Angles
Somethings you need to know about triangles...
-The sum of interior angles (all 3 angles in a triangle) in a triangle is 180 degrees
-if a triangle is equilateral (all sides are the same) then all the angles are equal
-if a triangle is isosceles (2 sides are the same) then 2 of the angles are equal
- if a triangle is scalene ( no sides are the same) then no angles are equal
Some things you need to know about quadrilaterals...
-the sum of interior angles (all 4 angles in a quadrilateral) in a quadrilaterial is 360
degrees
-in parallelograms (opposite sides are equal and parallel) opposite angles are always
equal
-in parallelograms adjacent (next to) sides are always supplementary (add up to 180
degrees)
Somethings you need to know about polygons...
-you can find the sum of interior angles (all the angles in any polygon) in any polygon by
using diagonals to break it into triangles
To find the missing angle in a triangle:
1. add up the measure of the angles you know
2. subtract from 180 degrees (sum of interior angles)
3. The difference is the missing angles
Example 1:Two angle measurements in a triangle are 63 degrees and 98 degrees. What is
the measure of the third angle?
step 1. 63 + 98 = 161 step 2. 180 - 161 = 19 step 3. 19 degrees is the answer
Example 2: An isosceles triangle has one angle measuring 90 degrees. What is the
measure of the 2nd angle?
Since this is an isosceles triangle that means two sides as well as two angles are equal to
each other. So I have to start by subtracting what I know (the 90 degrees) from 180
degrees (the sum of interior angles).
180 - 90 = 90
The 90 degrees represents the measurement of both the other two
angles in the triangle. So, to find the measure of the 2nd one all by itself I need to divide
90 by 2. I can divide by 2 because I know they are equal to each other.
90 / 2 = 45 So, 45 degrees is the measure of the 2nd angle. 45 degrees is the answer
To find the missing angle in a quadrilateral:
1. add up the measure of the angles you know
2. subtract from 360 degrees (sum of inteiror angles)
3. The difference is the missing angles
Example 1: Three angle measurements in a quadrilateral are 53 degrees, 98 degrees, and
162 degrees. What is the measure of the fourth angle?
step 1. 53 + 72 + 162 = 287 step 2. 360 - 287 = 73 step 3. 73 degrees is the answer