[tex]\begin{gathered} y=3x^4-15x^2 \\ y=3x^2(x^2-5) \\ y=7x^3-35x \\ y=7(x^2-5) \\ commonfactoris(x^2\text{-5)} \\ \text{HCF}=(x^2\text{-5}) \\ \text{LCM}=3x^2\times7\times(x^2\text{-5}) \\ =21x^2\times(x^2\text{-5}) \\ =(21x^4-105x^2) \end{gathered}[/tex]
