Tính: (3/4x + 2y) (3/4x -2y)

Làm tính.
$a) \left(\frac{3}{4}x+2y\right)\left(\frac{3}{4}x-2y\right)$
$b) \left(7x+\frac{1}{5}\right)\left(7x-\frac{1}{5}\right)$$c) \left(4u^{2}v-3u{v}^3\right)\left(3u{v}^3+4u^{2}v\right)$
$d) \left(a+b-c\right)\left(a-b+c\right)$