Use a calculator to evaluate $\cos ^ { - 1 } ( - 0.81 )$ .Round your answer to two decimal places.
A)0.68
B) $- 0.89$
C)0.72
D) $- 0.94$
E)2.51

Question

Quizplus · Accepted Answer

The correct answer is obtained by calculating the inverse cosine (or arccos) of -0.81. The inverse cosine function returns the angle whose cosine is the given number. Since the cosine function ranges from -1 to 1 over its domain, and considering the range of the arccos function is from 0 to π radians (or 0 to 180 degrees), the result for $\cos^{-1}(-0.81)$ will be an angle in radians between π/2 and π (or 90 and 180 degrees in degrees) because cosine is negative in the second quadrant. When calculated, $\cos^{-1}(-0.81)$ is approximately 2.51 radians, which matches choice E.

Use a Calculator to Evaluate cos⁡−1(−0.81)\cos ^ { - 1 } ( - 0.81 )cos−1(−0.81)

Use a Calculator to Evaluate $\cos ^ { - 1 } ( - 0.81 )$