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JEE Mains · Maths · STD 12 - 5. continuity and differentiation

यदि \(y =\sum_{ k =1}^{6} k \cos ^{-1}\left\{\frac{3}{5} \cos kx -\frac{4}{5} \sin kx \right\}\), तो \(x =0\) पर \(\frac{ dy }{ dx }\) का मान है -

  1. A \(90\)
  2. B \(91\)
  3. C \(88\)
  4. D \(89\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(91\)

Step-by-step Solution

Detailed explanation

Put \(\cos \alpha=\frac{3}{5}, \sin \alpha=\frac{4}{5} \quad 0<\alpha<\frac{\pi}{2}\) Now \(\frac{3}{5} \cos kx -\frac{4}{5} \sin kx\) \(=\cos \alpha \cdot \cos kx -\sin \alpha \cdot \sin kx\) \(=\cos (\alpha+k x)\) As we have to find derivate at \(x=0\) We have…
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