（x+2y)(x-2y)+(x+1)(x-1) x(x-1)-(x-1/3)(x+1/3)
=x²-4y²+(x²-1)(x-1)-x²+1/9
= -4y²+x³-x-x²+1
=1-4y²

x(x+1)+(2-x)(2+x)
=x²+x+4-2x+2x-x²
=x²+x+4-x²
=x+4
(a+1/2b)(a-1/2b)-(3a-2b)(3a+2b)
=a²+1/2ab-1/2ab-1/4b²-9a²+6ab-6ab+4b²
=a²-1/4b²-9a²+4b²
=13/4b²-8a²