Which sum or difference identity would you use to verify that sin (90° +θ)=cosθ?
A) sin(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
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sin(a + b) = sin(a)cos(b) + cos(a)sin(b)
sin(90º + x) = sin(90º)cos(x) + cos(90º)sin(x) = cos(x)