a) \(A=x^2-8x-y^2-8y\)
\(A=\left(x^2-y^2\right)-\left(8x+8y\right)\)
\(A=-8\left(x-y\right)\left(x+y\right)\)
b) \(B=x^2-6x+9-4y^2\)
\(B=\left(x-3\right)^2-\left(2y\right)^2\)
\(B=\left(x-3-2y\right)\left(x-3+2y\right)\)
c) \(C=7x-7y-ax+ay\)
\(C=7\left(x-y\right)-a\left(x-y\right)\)
\(C=\left(x-y\right)\left(7-a\right)\)
\(A=\left(x^2-8x+16\right)-\left(y^2+8y+16\right)=\left(x-4\right)^2-\left(y+4\right)^2=\left(x-4+y+4\right)\left(x-4-y-4\right)=\left(x+y\right)\left(x-y-8\right)\)
\(B=\left(x^2-6x+9\right)-4y^2=\left(x-3+2y\right)\left(x-3-2y\right)\)
\(C=7\left(x-y\right)-a\left(x-y\right)=\left(7-a\right)\left(x-y\right)\)
