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Transform an exponential series without differentiating again

Let y=e1/(x+1)y=e^{1/(x+1)}. Show that yy′′−(y′)2=2y2(x+1)3yy^{\prime\prime}-(y^\prime)^2=\dfrac{2y^2}{(x+1)^3}. Hence find its Maclaurin expansion through x2x^2, and deduce the expansion of e−x/(x+1)e^{-x/(x+1)} through x2x^2.

[2007/HCI/I/8]

CJC · Discussion · Question 10

Logarithmic differentiation gives a simple derivative relation.

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