A solid rectangular block has a base which measures $2x$ cm by $x$ cm. The height of the block is $y$ cm
and the volume of the block is $72 cm^3$. Express $y$ in terms of $x$ and show that the total surface area, $Acm^2$
, of the block is given by $$A=4x^2+\frac{216}{x}$$
My attempt,
$2x^2y=72$
$y=\frac{36}{x^2}$
$A=2\cdot2x^2+4yx$
$A=4x^2+\frac{144}{x}$
Where have I done mistake?
Best Answer
The surface area is:
$$A = 2*(2x^2 + 2xy + xy) = 4x^2 + 6xy= 4x^2 + \frac{216}{x}$$