Question

Find the measure of the exterior angle.

Answer 1

138°

Explanation:

An exterior angle has the same measure as the sum of the two opposite interior angles. Insert the two given interior angles as the sum of the exterior angle:

`60+(x+9)=2x`

Simplify the equation. Solve for x, then insert the value of x into the value of the exterior angle.

Simplify parentheses:

`60+x+9=2x`

Combine like terms by addition or subtraction as necessary:

`(60+9)+x=2x\\\\69+x=2x`

Get the variables on the same side. Use inverse operations. Subtract x from both sides:

`69+1x-1x=2x-1x\\\\69=1x\\\\69=x`

The value of x is 69. Insert into the value of the exterior angle*:

`2(69)`

Simplify:

`2*69\\\\138`

The measure of the exterior angle is 138°.

:Done

*You can also insert the value of x into (x+9) and then add the simplified value to the other interior angle, 60:

`60+(69+9)\\\\60+78=138`

Answer 2

60 + (x+9) = 2x because of exterior angle theorem so x=69 i believe