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**coyoteflare** a cuboid has the square base of side $\displaystyle xcm$ and height $\displaystyle hcm$. its volume is $\displaystyle 120cm^3$.

i) find $\displaystyle h$ in terms of $\displaystyle x$. Hence show that the surface area, $\displaystyle Acm^2$, of the cuboid is given by $\displaystyle A = 2x^2 + \frac{480}{x}$ .

ii) find $\displaystyle \frac{dA}{dx}$ and $\displaystyle \frac{d^2A}{dx^2}$

iii) Hence find the value of $\displaystyle x$ which gives the minimum of surface area. Find also the value of the surface area in this case.