Question

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 b
b. sin (a +b) = sin a cos b + cos a sin b
c. sin (a -b) = sin a cos b- cos a sin b
d. cos (a +b) = cos a cos b - sin a sin b

Answer 1

the guy above is correct

Explanation:

I took the test

Answer 2

b. sin (a +b) = sin a cos b + cos a sin b

Explanation:

Since you're trying to prove a relation involving the sine of a sum, that is the identity you would use:

sin (a +b) = sin a cos b + cos a sin b

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sin(90° +q) = sin(90°)cos(q) +cos(90°)sin(q)

= 1·cos(q) +0·sin(q)

= cos(q)