Explain and use the complementary-angle relationship between sine and cosine.
Rewrite a sine expression as the cosine of its complementary angle
Problem
Calculate the complement of \(25°\) and apply \(\sin(θ)=\cos(90°-θ)\) to rewrite \(\sin(25°)\) as a cosine expression.
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What this problem is really about
A sine-to-cosine rewrite uses the angle’s complement, not its supplement or the original angle. We’ll state the cofunction identity, subtract the given acute angle from ninety degrees, and place that computed complement inside the cosine expression.
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