$${ \left( \frac{ 3 }{ 4 } x- \frac{ y }{ 3 } \right) }^{ 2 } =$$
$\frac{\left(9x-4y\right)^{2}}{144}$
$-\frac{xy}{2}+\frac{9x^{2}}{16}+\frac{y^{2}}{9}$
