64x⁴ + 16x²y² + y⁴ - 16x²y²
= (8x²)² + 2.8x².y² + (y²)² - (4xy)²
= (8x² + y²)² - (4xy)²
= (8x² - 4xy + y²)(8x² + 4xy + y²)
\(64x^4+y^4\)
\(=64x^4+16x^2y^2+y^4-16x^2y^2\)
\(=\left(8x^2\right)^2+2.8x^2.y^2+y^4-\left(4xy\right)^2\)
\(=\left(8x^2+y^2\right)^2-\left(4xy\right)^2\)
\(=\left(8x^2-4xy-y^2\right)\left(8x^2+4xy-y^2\right)\)