\(a,4x^2-4y^2-20x+20y=4\left(x^2-y^2\right)-\left(20x-20y\right)=4\left(x-y\right)\left(x+y\right)-20\left(x-y\right)=\left(x-y\right)\left(4x+4y-20\right)=4\left(x-y\right)\left(x+y-5\right)\\ b,16x^2-25+\left(4x-5\right)=\left(4x-5\right)\left(4x+5\right)+\left(4x-5\right)=\left(4x-5\right)\left(4x+5+1\right)=\left(4x-5\right)\left(4x+6\right)=2\left(4x-5\right)\left(2x+3\right)\)
\(c,\left(x+5y\right)^3=x^3+15x^2y+75xy^2+125y^3\\ e,x^2-4x+4-y^2=\left(x-2\right)^2-y^2=\left(x-y-2\right)\left(x+y-2\right)\\ g,x^2-3x-4=\left(x^2-4x\right)+\left(x-4\right)=x\left(x-4\right)+\left(x-4\right)=\left(x+1\right)\left(x-4\right)\)
