1: \(=\left(25x^2-9y^2\right)\left(25x^2+9y^2\right)\)
\(=\left(25x^2+9y^2\right)\left(5x-3y\right)\left(5x+3y\right)\)
2: \(=\left(8x^3-y^3\right)\left(8x^3+y^3\right)\)
\(=\left(2x-y\right)\left(2x+y\right)\left(4x^2+2xy+y^2\right)\left(4x^2-2xy+y^2\right)\)