If $\sin(40°) = k$, what is $\cos(50°)$ in terms of $k$?
A$1 - k$
B$\frac{1}{k}$
C$k$
D$-k$
Answer & Solution
Correct answer: C. $k$
$40°$ and $50°$ are complementary ($40 + 50 = 90$). For complementary angles, $\sin\theta = \cos(90° - \theta)$, so $\cos 50° = \sin 40° = k$.
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