\(a^2-b^2-5a+5b=\left(a+b\right)\left(a-b\right)-5\left(a-b\right)=\left(a+b-5\right)\left(a-b\right)\)
\(x^2-6xy+9y^2-25=\left(x-3y\right)^2-5^2=\left(x-3y+5\right)\left(x-3y-5\right)\)
\(49-x^2-y^2+2xy=7^2-\left(x-y\right)^2=\left(7-x+y\right)\left(7+x-y\right)\)