![10](/tpl/images/0358/4844/07bbc.png)
Step-by-step explanation:
m∠2 and m∠1 are congruent by the Corresponding Angles Theorem; we set both expressions equal to each other:
[80 - x]° = [90 - 2x]°
+ x° + x°
______________
80° = [90 - x]°
-90° - 90°
__________
−10° = [−x]°
![10° = x](/tpl/images/0358/4844/866bf.png)
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