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MATHEMATICS · Single correct · AP · Calculus AB · Differentiation: Definition and Fundamental Properties · Differentiation: Definition and Fundamental Properties

Problem

If f(x)=cos⁡x⋅cos⁡2x⋅cos⁡4x⋅cos⁡8x⋅cos⁡6xf(x)=\cos x\cdot\cos2x\cdot\cos4x\cdot\cos8x\cdot\cos6x, then f′(π4)f'\left(\frac{\pi}{4}\right) is (1) 2\sqrt2 (2) −12-\frac{1}{\sqrt2} (3) 11 (4) None of these

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