In a geometric diagram, angle A and angle B are complementary, and they form a straight line with angle C. If angle A=x°, angle B=(2x)°, and angle C=90°, what is the measure of angle B?
Since angle A and angle B are complementary, we have the equation:
angle A + angle B = 90°.
Substituting the given values, we get:
x° + (2x)° = 90°.
Simplifying the equation, we have:
3x° = 90°.
Dividing both sides by 3, we find:
x° = 30°.
Therefore, the measure of angle B is 2x° = 2(30°) = 60°. Answer: \boxed{60}.