\(\left(6x^2+y^2\right)\left(y^2-6x^2\right)\)
\(=\left(y^2+6x^2\right)\left(y^2-6x^2\right)\)
\(=\left(y^2\right)^2-\left(6x^2\right)^2\)
\(=y^4-36x^4\)
\(\left(6x^2+y^2\right)\left(y^2-6x^2\right)\\ =\left(y^2\right)^2-\left(6x^2\right)^2=y^4-36x^4\)


