a) \(8x^3+y^3\)
\(=\left(2x\right)^3+y^3\)
\(=\left(2x+y\right)\left[\left(2x\right)^2-2x\cdot y+y^2\right]\)
\(=\left(2x+y\right)\left(4x^2-2xy+y^2\right)\)
b) \(25-x^2y^2\)
\(=5^2-\left(xy\right)^2\)
\(=\left(5-xy\right)\left(5+xy\right)\)
c) \(x^2-6x+9\)
\(=x^2-2\cdot3\cdot x+3^2\)
\(=\left(x-3\right)^2\)