\(=4a^4+4a^2b^2+b^4-4a^2b^2\\ =\left(2a^2+b^2\right)^2-\left(2ab\right)^2\\ =\left(2a^2+b^2+2ab\right)\left(2a^2+b^2-2ab\right)\)
\(4a^4+b^4\)
\(=\left(2a^2\right)^2+\left(b^2\right)^2\)
\(=\left[\left(2a^2\right)^2+4a^2b^2+\left(b^2\right)^2\right]-4a^2b^2\)
\(=\left[2a^2+b^2\right]^2-\left(2ab\right)^2\)
\(=\left(2a^2+b^2+2ab\right)\left(2a^2+b^2-2ab\right)\)