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Question
If y = `log ((1 - x^2)/(1 + x^2))`, then `"dy"/"dx"` is equal to ______.
Options
`(4x^3)/(1 - x^4)`
`(-4x)/(1 - x^4)`
`1/(4 - x^4)`
`(-4x^3)/(1 - x^4)`
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Solution
If y = `log ((1 - x^2)/(1 + x^2))`, then `"dy"/"dx"` is equal to `(-4x)/(1 - x^4)`.
Explanation:
Given that: y = `log ((1 - x^2)/(1 + x^2))`
⇒ y = log(1 – x2) – log(1 + x2) ....`[because log x/y = log x - log y]`
Differentiating both sides w.r.t. x
`"dy"/"dx" = 1/(1 - x^2) * "d"/"dx"(1 - x^2) - 1/(1 + x^2) (1 + x^2)`
= `(-2x)/(1 - x^2) - (2x)/(1 + x^2)`
= `(-2x - 2x^3 - 2x + 2x^3)/((1 - x^2)(1 + x^2))`
= `(-4x)/(1 - x^4)`.
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