Question

Let $f_{k}=\frac{1}{k} \bigg (\sin^{k}x+\cos^{k}x \bigg )$ where x ∈ R and k ≥ 1. Then $f_{4}(x)-f_{6}(x)$ equals
(a) $\frac{1}{4}$
(b) $\frac{1}{12}$
(c) $\frac{1}{6}$
(d) $\frac{1}{3}$

Answer 1

answer is a

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