(x-8y)(x-8y)+(x-8y)(x+8y)=x^2-16xy+64y^2+x^2-64y^2=2x^2-16xy
2×7.5^2-16×7.5×(-1.25)=112.5-(-150)=262.5
(x-8y)(x-8y)+(x-8y)(x+8y)=x^2-16xy+64y^2+x^2-64y^2=2x^2-16xy
2×7.5^2-16×7.5×(-1.25)=112.5-(-150)=262.5