(х-4)²-(x+1)(x+2)=
5(а+в)²-10ав=

(x-4)²-(x+1)(x+2)=x²-8x+16-(x²+3x+2)=x²-8x+16-x²-3x-2=-11x+145(a+b)²-10ab=5(a²+2ab+b²)-10ab=5a²+10ab+5b²-10ab=5a²+5b²