Which expression is equivalent to cosine of open paren pi over 2 plus r close paren for all values of r ?
Answer
A
cosine of r
B
negative cosine times r
C
sine of r
D
negative sine times r
Explanation
Using the angle-sum identity, cos(π/2 + r) = cos(π/2)cos(r) − sin(π/2)sin(r). Since cos(π/2) = 0 and sin(π/2) = 1, this simplifies to −sin(r), which is choice D.
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