1 (a+3)(a-3)2 -(x-y)²3 (a+3)(a-4)4 a^2+b^2-4a^2b^2\x09=a^2+b^2-4a^2b^2+2ab-2ab\x09=(a+b)^2-4a^2b^2-2ab\x09=(a+b)^2-4a^2b^2-2ab+1/4-1/4\x09=(a+b)^2-(2ab+1/2)^2+1/4\x09=(a+b+2ab+1/2)(a+b-2ab-1/2)+1...