3X^4-48y^4
=3（x^2+4y^2)(x+2y)(x-2y)
(x+1)^2-9(x-1)^2
=(x+1+3x-3)(x+1-3x+3)
=(4x-2)(4-2x)
=4(x-1)(1-x）
x^2+4xy+3y^2
=（x+2y)^2-y^2
=(x+3y)(x-y)