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Differentiate the following w.r.t.x: cos2[log(x2 + 7)] - Mathematics and Statistics

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Question

Differentiate the following w.r.t.x: cos2[log(x2 + 7)]

Sum
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Solution

Let y = cos2[log(x2 + 7)]
Differentiating w.r.t. x, we get
`"dy"/"dx" = "d"/"dx"{cos[log(x^2 + 7)]}^2`

= `2cos[log(x^2 + 7)]."d"/"dx"{cos[log(x^2 + 7)]}`

= `2cos[log(x^2 + 7)].{-sin[log(x^2 + 7)]}."d"/"dx"[log(x^2 + 7)]`

= `-2sin[log(x^2 + 7)].cos[log(x^2 + 7)] xx (1)/(x^2 + 7)."d"/"dx"(x^2 + 7)`

= `-sin[2log(x^2 + 7)] xx (1)/(x^2 + 7).(2x + 0)`  ...[∵ 2sinx · cosx = sin2x]

= `(-2x.sin[2log(x^2 + 7)])/(x^2 + 7)`.

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Chapter 1: Differentiation - Exercise 1.1 [Page 12]

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