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NCERT Class XI Mathematics - Limits and Derivatives - Solutions

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Question : 53 of 72
Marks: +1, -0
ax4−bx2\frac{a}{x^4} - \frac{b}{x^2} + cos x
Solution:  
Let f (x) = ax4−bx2\frac{a}{x^4} - \frac{b}{x^2} + cos x
⇒ f (x) = ax−4−bx−2+cos⁡xa x^{-4} - b x^{-2} + \cos x ... (i)
Differentiating (i) with respect to x, we get
ddx\frac{d}{dx} [f (x)] = a(−4)x−5−b(−2)x−3a(-4)x^{-5} - b(-2)x^{-3} + (- sin x) = −4ax5+2bx3−sin⁡x\frac{-4a}{x^5} + \frac{2b}{x^3} - \sin x
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