Given:
Vertical angles.
One angle is 85°.
To find:
The measure of ∠1, ∠2 and ∠3.
Solution:
∠2 and 85° are vertically opposite angles and ∠1 and ∠3 are vertically opposite angles.
Vertical angle theorem:
If two lines are intersecting, then the vertically opposite angles are congruent.
⇒ m∠2 = 85°
Sum of the adjacent angles in a straight line = 180°
m∠2 + m∠3 = 180°
85° + m∠3 = 180°
Subtract 85° from both sides.
85° + m∠3 - 85° = 180° - 85°
m∠3 = 95°
By vertical angle theorem:
⇒ m∠1 = m∠3
⇒ m∠1 = 95°
Therefore m∠1 = 95°, m∠2 = 85° and m∠3 = 95°.