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Find dy/dx for the given function: y^x = x^y

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Question

Find `bb(dy/dx)` for the given function:

yx = xy

Sum
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Solution

Given, yx = xy

Taking logarithm of both sides,

log yx = log xy

x log y = y log x  ...(i)

Differentiating (i) w.r.t. x,

`x d/dx log y + log y d/dx (x)= y d/dx log x + log x d/dx y`

`=> x xx 1/y dy/dx + log y xx 1 = y xx 1/x + log x dy/dx`

`=> x/y dy/dx + log y = y/x + log x dy/dx`

`=> x/y dy/dx - log x dy/dx = y /x - log y` 

`=> dy/dx (x/y - log x) = y /x - log y`   ...(ii)

On multiplying both sides of (ii) by xy, we get

`=> dy/dx (x^2 - xy log x) = y ^2 - xy log y`

`therefore dy/dx = (y ^2 - xy log y)/(x^2 - xy log x)`

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Chapter 5: Continuity and Differentiability - Exercise 5.5 [Page 178]

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NCERT Mathematics Part 1 and 2 [English] Class 12
Chapter 5 Continuity and Differentiability
Exercise 5.5 | Q 13 | Page 178

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