Question

What is the measure of an angle if the measures of its two adjacent supplementary angles add up to 100°?

Answer 1

Answer:  130

Explanation:

Let x be the unknown angle we want to find.

Let y be adjacent and supplementary to x. This means x+y = 180

Let z also be adjacent and supplementary to x. So x+z = 180 also

Subtracting the two equations leads to y-z = 0 and y = z. So effectively we've proven the vertical angle theorem.

Since the supplementary angles to x add to 100, we know that y+z = 100. Plug in y = z and solve for z

y+z = 100

z+z = 100

2z = 100

z = 100/2

z = 50

Therefore,

x+z = 180

x+50 = 180

x = 180-50

x = 130