$\dfrac{d}{dx}(\tan x)$ equals:
A$\cot x$
B$\sec x \tan x$
C$-\sec^2 x$
D$\sec^2 x$
Answer & Solution
Correct answer: D. $\sec^2 x$
$\tan x = \sin x/\cos x$; quotient rule gives $(cos^2 + sin^2)/\cos^2 x = 1/\cos^2 x = \sec^2 x$.
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