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Find the second order derivatives of the following : x3.logx

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Question

Find the second order derivatives of the following : x3.logx

Sum
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Solution

Let y = x3.logx

Then, `"dy"/"dx" = "d"/"dx"(x^3.logx)`

= `x^3"d"/"dx"(logx) + (logx)."d"/"dx"(x^3)`

= `x^3 xx (1)/x + (logx) xx 3x^2`

= x2 + 3x2 log x
= x2(1 + 3 log x)
and
`(d^2y)/(dx^2) = "d"/"dx"[x^2(1 + 3logx)]`

= `x^2."d"/"dx"(1 + 3logx) + (1 + 3logx) xx 2x`

= `x^2(0 + 3 xx 1/x) + (1 + 3logx) xx 2x`

= 3x + 2x + 6x log x
= 5x + 6x log x 
= x(5 + 6 log x).

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Chapter 1: Differentiation - Exercise 1.5 [Page 60]

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