Answer:
138°
Step-by-step 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:
[tex]60+(x+9)=2x[/tex]
Simplify the equation. Solve for x, then insert the value of x into the value of the exterior angle.
Simplify parentheses:
[tex]60+x+9=2x[/tex]
Combine like terms by addition or subtraction as necessary:
[tex](60+9)+x=2x\\\\69+x=2x[/tex]
Get the variables on the same side. Use inverse operations. Subtract x from both sides:
[tex]69+1x-1x=2x-1x\\\\69=1x\\\\69=x[/tex]
The value of x is 69. Insert into the value of the exterior angle*:
[tex]2(69)[/tex]
Simplify:
[tex]2*69\\\\138[/tex]
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:
[tex]60+(69+9)\\\\60+78=138[/tex]
