三道因式分解题

n(n+1)(n+2)(n+3)+1=(n^2+3n+1)^2;3x^2+5xy-2y^2+x+9y-4=(3x-y+4)(x+2y-1);(x-2)^4+(x-6)^4-626=2(x-7)(x-1)(x^2-8x+49).