2.10: Quotient rule and small change for a logarithmic ratio

0606/21/M/J/19 — Question 2 · 5 marks

Two variables xx and yy are such that y=lnxx3y = \dfrac{\ln x}{x^{3}} for x>0x > 0.
(i)
Show that dydx=13lnxx4\dfrac{\mathrm{d}y}{\mathrm{d}x} = \dfrac{1 - 3\ln x}{x^{4}}.
[3]
(ii)
Hence find the approximate change in yy as xx increases from e\mathrm{e} to e+h\mathrm{e} + h, where hh is small.
[2]