Find the expression as the cosine of an angle.

Question

Find the expression as the cosine of an angle. ​
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Quizplus · Accepted Answer

The expression can be written as cos(arccos(11/13)), using the inverse cosine function. Simplifying this expression using the cosine of a supplementary angle identity yields cos(180° - arccos(11/13)), which equals cos(arccos(-11/13)), since cosine is an even function. Therefore, the expression is equivalent to cos(theta), where theta = arccos(-11/13). The exact value of theta is approximately 131.8 degrees in the fourth quadrant, which confirms that the cosine of this angle is negative. Since choice C is the only option with a negative coefficient in the exponent, it must be the correct answer.

Find the Expression as the Cosine of an Angle