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If xsqrt(1+y) + y  sqrt(1+x) = 0, for, −1 < x < 1, prove that dy/dx = -1/(1+ x)^2. - Mathematics

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Question

If `xsqrt(1+y) + y  sqrt(1+x) = 0`, for, −1 < x < 1, prove that `dy/dx = -1/(1+ x)^2`.

Theorem
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Solution

`x sqrt(1 + y) + y sqrt(1 + x) = 0`

∴ `xsqrt(1 + y) = - y sqrt(1 + x) = 0`

On squaring both sides,

x2 (1 + y) = y2 (1 + x)

⇒ x2 + x2y = y2 + y2x

⇒ x2 – y2 – y2x + x2y = 0

⇒ (x – y)(x + y) + xy(x – y) = 0

⇒ (x – y)[x + y + xy] = 0

x – y = 0 ⇒ x ≠ y

x + y (1 + x) = 0

∴ y = `-x/(1 - x)`

∴ `dy/dx = ((1 + x)(1) - x * 1)/(1 + x)^2`

= `-(1 + x - x)/(1 + x)^2`

= `-1/(1 + x)^2`

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Chapter 5: Continuity and Differentiability - Exercise 5.9 [Page 191]

APPEARS IN

NCERT Mathematics Part 1 and 2 [English] Class 12
Chapter 5 Continuity and Differentiability
Exercise 5.9 | Q 14 | Page 191

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