(х+5)^2-(x-4)(x+4)+(x-3)(x+7)=x^2+10x+25-(x^2-16)+x^2+7x-3x-21= x^2+10x+25-x^2+16+x^2+4x-21=x^2+14x+20
(х+5)^2-(x-4)(x+4)+(x-3)(x+7)=x^2+10x+25-(x^2-16)+x^2+7x-3x-21= x^2+10x+25-x^2+16+x^2+4x-21=x^2+14x+20