Math 8: Triangles and Angle Measures
Section #3: Vertical Angles
Corresponds with 7th grade Module 6, Lesson 1- 4
Notes # 35
_
Vertical angles are formed whenever two straight lines cross or intersect. The angles opposite or
across from each other are
____________
(____________in size).
 < a & < c are _____________ angles, therefore m< a  m< c
b
a
c
 < b & < d are _____________ angles, therefore m< b  m< d
d
Example # 1 Two lines meet at a point. In a complete sentence, describe the relevant angle
relationships in the diagram. Find the values of 𝑟, 𝑠, and 𝑡.
a.) Angle r and angle t must be
to
each other because they are
r°
angles.
s°
b.) The value of angle s must be
t°
because
it’s ________________ to an angle of the same measure.
c.) All non-vertical angles must be _____________________
because they next to each other on and form straight line.
Example # 2 Two lines meet at the vertex of a ray. Set up and solve an equation to find 𝑎.
49°
33°
a°
Example # 3 Two lines meet at a point. Set up and solve an equation to find the value of 𝑥.
Then check your answer by finding the value of the angle (x + 15)°.
72°
(x+15)°
25°
You Try:
1) Find the measure of angles x, y, & z.
x
26˚
y
z
2) Three lines meet at a point. Find the measure of angle a and b and state your reasoning for them.
Use an equation to find the value of c.
78°
b
°
52°
a°
c
°
a
°
3) Find the value of y using an equation. Prove your answer is correct by finding the value of the
unknown angle.
118°
3y + 19°