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Single Variable Calculus

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Moderate

Fun With Trigonometric Terms and the Quotient Rule

SVCALC-SKPKZK

Find $f'(-\frac {\pi }{ 4 } )$ for:

$$f(x)=\frac { cosx-sinx }{ tanx } $$

A

$\sqrt { 2 } $

B

$-\sqrt { 2 }$

C

$2\sqrt { 2 }$

D

$-2\sqrt { 2 }$