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If y = xxx...∞, show that dydxdydx=y2x(1-logy).. - Mathematics and Statistics

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Question

If y = `x^(x^(x^(.^(.^.∞))`, then show that `"dy"/"dx" = y^2/(x(1 - logy).`.

Sum
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Solution

y = `x^(x^(x^(.^(.^.∞))`
∴ log y = `log(x^(x^(x^(.^(.^.∞)))))`
= `x^(x^(x^(.^(.^.∞)))).logx` 
∴ log y = y log x                       ...(1)
Differentiating both sides w.r.t. x, we get
`(1)/y.dy/dx = y.d/dx(logx) + (logx)dy/dx`

∴ `(1)/ydy/dx = y xx (1)/x + (logx)dy/dx`

∴ `(1/y - logx)dy/dx = y/x`

∴ `((1 - ylogx)/(y))dy/dx"= y/x`

∴ `dy/dx = y^2/(x(1 - ylogx)`

∴ `dy/dx = y^2/(x(1 - logy)`.                 ...[By (1)]

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Chapter 1: Differentiation - Exercise 1.3 [Page 40]

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