a) \(4x^2\left(x+3\right)-8x\left(3+x\right)=4x\left(x+3\right)\left(x-2\right)\)
b) \(4x^2+y^2-25+4xy=\left(2x+y\right)^2-25=\left(2x+y-5\right)\left(2x+y+5\right)\)
c) \(\left(x-3\right)^2-\left(x+2\right)^2=\left(x-3-x-2\right)\left(x-3+x+2\right)=-5\left(2x-1\right)\)