In a right triangle, if $\sin\theta = \frac{3}{5}$, what is the value of $\cos\theta$ (assuming $\theta$ acute)?
A$\frac{4}{5}$
B$\frac{5}{3}$
C$\frac{5}{4}$
D$\frac{3}{4}$
Answer & Solution
Correct answer: A. $\frac{4}{5}$
$\sin^2 + \cos^2 = 1 \Rightarrow \cos^2 = 1 - 9/25 = 16/25 \Rightarrow \cos\theta = 4/5$ (taking positive root for acute angle).
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