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If y = tanx + secx, prove that ddd2ydx2=cosx(1-sinx)2

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Question

If y = tanx + secx, prove that `("d"^2y)/("d"x^2) = cosx/(1 - sinx)^2`

Sum
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Solution

We have y = tanx + secx.

Differentiating w.r.t. x, we get

`("d"y)/("d"x)` = sec2x + secx tanx

= `1/(cos2x) + sinx/(cos^2x)`

= (1 + sinx)/(cos^2x)`

= `(1 + sinx)/((1 + sinx)(1 - sinx))`

Thus `("d"y)/("d"x) = 1/(1 - sin )`.

Now, differentiating again w.r.t. x, we get

`("d"^2y)/("d"x^2) = (-(cos x))/(1 - sin x)^2`

= `cosx/(1 - sin x)^2`

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Chapter 5: Continuity And Differentiability - Solved Examples [Page 96]

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NCERT Exemplar Mathematics Exemplar [English] Class 12
Chapter 5 Continuity And Differentiability
Solved Examples | Q 14 | Page 96

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