x^{2} +16xy+63y ^{2}
\(x^{2} +16xy+63y ^{2} \\ = x^{2} +16xy+64y ^{2}-y ^{2} \\ = (x+8y)^{2}-y ^{2} \\ =(x+8y+y)(x+8y-y) \\ =(x+9y)(x+7y)\)
