(2a+3b)(-2a+3b)
=(3b)^2-(2a)^2
=9b^2-4a^2;
(x-1)(x+3)-x(x+5)-8
=x^2+2x-3-x^2-5x-8
=-3x-11;
(2a-b+1)(b+2a-1)
= [2a-(b-1)][2a+(b-1)]
=(2a)^2-(b-1)^2
=4a^2-(b^2-2b+1)
=4a^2-b^2+2b-1;
(3a-2b+c)²
=(3a)^2+(2b)^2+c^2-2*(3a)*(2b)+2*(3a)*c-2*(2b)*c
=9a^2+4b^2+c^2-12ab+6ac-4bc.