Answer:
x=70
Explanation:
Angle 1 will be 90° when it subtends a 180° arc. That means the sum of 100° and (x+10) must be 180°, so (x+10) = 80°.
We assume this is intended to mean ...
... (x +10)° = 80° . . . . . note the ° symbol added outside parentheses
... x +10 = 80 . . . . . divide by °
... x = 70 . . . . . . . . .subtract 10
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If the intent is (x+10°) = 80°, then x=70°.
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Comment on the numbers here
Units need to be properly specified in problems of this nature. As written, we probably should assume that 10 is radians, and x is a large negative number, about -8.60374 (radians), or -492.958°.
A number of radians is a "pure number." It has no units. The term "radians" is used to signify that the number is considered to be an angle measure.