Explain and use the complementary-angle relationship between sine and cosine.
Rewrite a cosine as the sine of its complementary angle
Problem
Calculate the complement of \(25°\) and apply \(\cos(θ)=\sin(90°-θ)\) to rewrite \(\cos(25°)\) as a sine expression.
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What this problem is really about
Switching from cosine to sine requires switching to the complementary acute angle as well. We’ll write the cofunction rule, calculate ninety degrees minus the given angle, and use that result as the sine argument while preserving the original value.
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