Mathematics · 2020
JEE Main · 2 September 2020, Shift 2 · Q72
If y=Σ_k =1^6 k cos^-1{3/5 cos k x-4/5 sin k x}, then (d y)/(d x) at x=0 is \ \ \ \.
If $\displaystyle y=\sum_{\mathrm{k}=1}^6 \mathrm{k} \cos ^{-1}\left\{\frac{3}{5} \cos \mathrm{k} x-\frac{4}{5} \sin \mathrm{k} x\right\}$, then $\displaystyle \frac{\mathrm{d} y}{\mathrm{~d} x}$ at $\displaystyle x=0$ is \_\_\_\_.
Official answer
91
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JEE Main 2020 Mathematics question, with the answer from NTA’s final answer key. Where our answers come from.