a: \(=5x\left(2xy^2+x^2y^4+1\right)\)
\(=5x\left(xy^2+1\right)^2\)
b: \(x^2-2=\left(x-\sqrt{2}\right)\left(x+\sqrt{2}\right)\)
c: \(250y^3-\dfrac{2}{27}x^3\)
\(=2\left(125y^3-\dfrac{1}{27}x^3\right)\)
\(=2\left(5y-\dfrac{1}{3}x\right)\left(25y^2+\dfrac{5}{3}xy+\dfrac{1}{9}x^2\right)\)