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Sec-1(14x3-3x),0<x<12

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Question

`sec^-1 (1/(4x^3 - 3x)), 0 < x < 1/sqrt(2)`

Sum
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Solution

Let y = `sec^-1 (1/(4x^3 - 3x))`

Put x = cos θ

∴ θ = `cos^-1x`

y = `sec^-1 (1/(4cos^3theta - 3 cos theta))`

⇒ y = `sec^-1 (1/(cos 3theta))`  .....[∵ cos 3θ = 4 cos3θ – 3 cos θ]

⇒ y = `sec^-1 (sec 3theta)`

⇒ y = 3θ

y = `3cos^-1x`

Differentiating both sides w.r.t. x

`"dy"/"d" = 3 * "d"/"dx" cos^-1x`

= `3((-1)/sqrt(1 - x^2))`

= `(-3)/sqrt(1 - x^2)`

Hence, `"dy"/"dx" = (-3)/sqrt(1 - x^2)`.

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Chapter 5: Continuity And Differentiability - Exercise [Page 110]

APPEARS IN

NCERT Exemplar Mathematics Exemplar [English] Class 12
Chapter 5 Continuity And Differentiability
Exercise | Q 41 | Page 110

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