\(ax+bx+ay+by\)
\(=x\left(a+b\right)+y\left(a+b\right)\)
\(=\left(x+y\right)\left(a+b\right)\)
\(xy+1-x-y\)
\(=x\left(y-1\right)-\left(y-1\right)\)
\(=\left(x-1\right)\left(y-1\right)\)
\(x^2-y^2-5x-5y\)
\(=\left(x+y\right)\left(x-y\right)-5\left(x+y\right)\)
\(=\left(x+y\right)\left(x-y-5\right)\)