a, \(14x^2-21x^2+28x^2y^2\)
\(=-7x^2+28x^2y^2=-7x^2\left(1-4y^2\right)\)
\(=-7x\left(1-2y\right)\left(1+2y\right)\)
b, \(8x^3+4x^2-y^3-y^2\)
\(=\left(8x^3-y^3\right)+\left(4x^2-y^2\right)\)
\(=\left(2x-y\right)\left(4x^2+2xy+y^2\right)+\left(2x-y\right)\left(2x+y\right)\)
\(=\left(2x-y\right)\left(4x^2+2xy+y^2+2x+y\right)\)