a,$\frac{1}{2}$ $x^{2}$ $y^{2}$ (4$x^{2}$ -$y^{2}$
=2$x^{4}$ $y^{2}$ -$\frac{1}{2}$ $x^{2}$ $y^{4}$
b,($\frac{1}{2}$ x-1)(2x-3)
=$\frac{1}{2}$ x.2x+$\frac{1}{2}$ x.(-3)-2x+3
=$x^{2}$ -$\frac{3}{2}$ x-2x+3
=$x^{2}$ -$\frac{7}{2}$ x+3
c,(x-7)(x-5)
=x.x+x.(-5)-7.x-7.(-5)
=$x^{2}$ -5x-7x+35
=$x^{2}$ -12x+35
d,(x-$\frac{1}{2}$ )(x+$\frac{1}{2}$ )(4x-1)
=($x^{2}$ -$\frac{1}{4}$ )(4x-1)
=$x^{2}$ .4x+$x^{2}$ .(-1)-$\frac{1}{4}$ .4x-$\frac{1}{4}$ .(-1)
=$4x^{3}$ -$x^{2}$ -x+$\frac{1}{4}$