Solve sinusoidal equations (basic)

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Jamie tried to solve the following equation, where

x

is in radians to the nearest hundredth, in the interval from

? π

π

, but she made a mistake.

\cos ? (x) = ? 0.08

Here is Jamie's work.

\begin{array}{rcl} \cos^{? 1} ? (\cos ? (x)) & = & \cos^{? 1} ? (? 0.08) \\ x & \approx & 1.65 \\ ↙ & ↘ \\ \begin{aligned} Using \cos ? (x) = \cos ? (x + 2 π) \\ x & \approx 1.65 + 2 π n \\ x & \approx \dots ? 4.63, 1.65, 7.93 \dots \end{aligned} & \begin{aligned} Using \cos ? (x) = \cos ? (π ? x) \\ and \cos ? (x) = \cos ? (x + 2 π) \\ x & \approx 1.49 + 2 π n \\ x & \approx \dots ? 4.79, 1.49, 7.77 \dots \end{aligned} \end{array}

The solutions to $x$ ? in the interval from $? π$ ? to $π$ ? are $x \approx 1.49$ ? and $x \approx 1.65$ ?.

What was Jamie's mistake?

(Choice A) ?
Jamie evaluated $\cos^{? 1} ? (? 0.08)$ ? in degrees instead of in radians.
(Choice B) ?
Jamie used an identity that only applies to the sine function, not to the cosine function.
(Choice C) ?
Jamie forgot to use negative $n$ ?-values which would reveal more solutions in the interval.
(Choice D) ?
Jamie gave solutions that were outside of the interval.

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