Which sum or difference identity would you use to verify that cos (180° - q) = -cos q?a.sin (a -b) = sin a cos b – cos a sin bb.cos (a -b) = cos a cos b – sin a sin bc.cos (a -b) = cos a cosb + sin a sin bd.sin (a + b) = sin a cos b + cos a sin b

Use the cosine difference identity, cos(a − b) = cos a cos b + sin a sin b. With a = 180° and b = q, this gives cos(180° − q) = cos 180° cos q + sin 180° sin q = (−1)cos q + 0 = −cos q. This is choice C.

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