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Find dydx, if x = (u+1u)2,y=(2)(u+1u) - Mathematics and Statistics

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Question

Find `"dy"/"dx"`, if x = `("u" + 1/"u")^2, "y" = (2)^(("u" + 1/"u"))`

Sum

Solution

x = `("u" + 1/"u")^2`      .....(i)

Differentiating both sides w.r.t. u, we get

`"dx"/"du" = 2("u" + 1/"u") * "d"/"dx" ("u" + 1/"u")`

`= 2("u" + 1/"u") [1 + (- 1) "u"^(-2)]`

∴ `"dx"/"du" = 2("u" + 1/"u")(1 - 1/"u"^2)`

`"y" = (2)^(("u" + 1/"u"))`       .....(ii)

Differentiating both sides w.r.t. u, we get

`"dy"/"du" = 2^(("u" + 1/"u")) log 2 "d"/"dx" ("u" + 1/"u")`

∴ `"dy"/"du" = log 2 * 2^(("u" + 1/"u")) (1 - 1/"u"^2)`

∴ `"dy"/"dx" = (("dy"/"du"))/(("dx"/"du")) = (2^(("u" + 1/"u")) log 2 (1 - 1/"u"^2))/(2("u" + 1/"u")(1 - 1/"u"^2))`

`= (2^(("u" + 1/"u")) log 2)/(2("u" + 1/"u"))`

∴ `"dy"/"dx" = ("y" log 2)/(2sqrt"x")`        ....[From (i) and (ii)]

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Derivatives of Parametric Functions
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Chapter 3: Differentiation - EXERCISE 3.5 [Page 97]

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