Question

∠A and ​ ∠B ​ are vertical angles with m∠A=x and m∠B=5x−80 . What is m∠A ?

Answer 1

Angle A's measure is 20.

Answer 2

we know that

Vertical Angles are the angles opposite each other when two lines cross. They are always congruent to one another

in this problem

∠A and ​ ∠B ​ are vertical angles

so

∠A=∠B ​

we have

∠A=$x\°$ 

∠B=$(5x-80)\°$

equate angle A and angle B

$x=5x-80$

solve for x

$5x-x=80$

$4x=80$

$x=20\°$

therefore

the answer is

the measure of angle A is $20\°$