1. Writing Equations to Find Missing Angles
Unit 7
Math 7

2. Objective-To find missing angles using rules of geometry.
Supplementary Angles-
Angles whose sum
is 180 . a b

3. Find the value of x. x 30
x = 180
x = 150

4. Find the supplement of the given angle.
1) 40
140
5) 89 91
2) 18
162
6) 23
157
3) 153 27
7) 131 49
4) 65
115
8) 118 62

5. Write a variable equation and solve.
Find an angle whose supplement
is 30 less than twice the angle. x
2x - 30
x + (2x - 30) = 180
3x - 30 = 180
3x = 210 70
x = 70

6. Complementary Angles sum is 90 . b a x+ 40 = 90 - 40 -40 x 40 x = 50
- Angles whose
sum is 90 . b a
x+ 40 = 90 x 40
x = 50

7. Find the complement of...
1) 20 70
2) 47 43
No complement
3) 100

8. Write a variable equation and solve.
Find an angle whose complement is 20
more than three times the angle.
x + 3x + 20 = 90 x
4x + 20 = 90
3x + 20
4x = 70
x = 17.5

9. angles of any triangle is always 180 . b
180 Rule for Triangles
- the sum of the interior
angles of any triangle is
always 180 . b 80 40 x a c
x = 180
x = 180
x = 60

10. Find each angle below.
y + 14 = 63
2y - 10
2y - 10 = 88
y = 29
y+14
y - 20
180
(y + 14) + (2y - 10) + (y - 20) = 180
4y - 16 = 180
4y = 196
y = 49

11. Vertical Angles Theorem
- the opposite angles
of intersecting lines
must be equal.

12. What’s the relationship between angles a and b?
Vertical Angles Theorem
- the opposite angles
of intersecting lines
must be equal.
Find the missing angles a, b and c.
What’s the relationship between angles a and b? 25
155 b c a
155 25

13. Find the missing angle. x 40 48
132