cos 15 0 o = cos ( 15 0 o − 36 0 o ) = cos ( − 21 0 o )
A n s w er : D
The expression equivalent to cos 150° is cos ( − 210° ) . Therefore, the correct answer is option D. This is because cos 150° can be expressed in terms of its reference angle and the properties of cosine values in different quadrants.
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