Which sum or difference identity would you use to verify that sin (90° + q) = cos q?a.cos (a -b) = cos a cos b + sin a sin bb.sin (a +b) = sin a cos b + cos a sin bc.sin (a -b) = sin a cos b- cos a sin bd.cos (a +b) = cos a cos b - sin a sin b

Use the sine sum identity: sin(a + b) = sin a cos b + cos a sin b. Set a = 90° and b = q. Since sin 90° = 1 and cos 90° = 0, this gives sin(90° + q) = 1·cos q + 0·sin q = cos q. This is choice B, sin(a + b) = sin a cos b + cos a sin b.

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