Question

7x(x-y+1)-7y(y-x-1)

Answer 1

7x(x-y+1)-7y(y-x-1)

=7x^2-7xy+7x-7y^2+7xy+7y

=7(x^2-y^2)+7(x+y)

=7(x+y)(x-y+1)

Answer 2

\(7x\left(x-y+1\right)-7y\left(y-x-1\right)\\ =7x\left(x-y+1\right)+7y\left(x-y+1\right)\\ =\left(7x+7y\right)\left(x-y+1\right)\\ =7\left(x+y\right)\left(x-y+1\right)\)