The identity $\sin 2A$ equals:
A$2\sin A\cos A$, the standard double-angle formula on the chart
B$\sin^2 A + \cos^2 A$, equal to $1$ by Pythagorean identity
C$2\sin^2 A$, missing the cosine factor in the formula
D$\sin A + \cos A$, the simple sum of the trig functions
Answer & Solution
Correct answer: A. $2\sin A\cos A$, the standard double-angle formula on the chart
Double-angle: $\sin 2A = 2\sin A\cos A$.
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