有幾條因式分解想請大家幫手解解

1)ab(c^2+d^2) + cd(a^2+b^2)= abc^2 + abd^2 + cda^2 + cdb^2= (abc^2 + cda^2) + (abd^2 + cdb^2)= ac(bc + ad) + bd(ad + cb)= (ac + bd)(bc + ad)orab(c^2+d^2) + cd(a^2+b^2)= abc^2 + abd^2 + cda^2 + cdb^2= (abc^2 + cdb^2) + (abd^2 + cda^2)= bc(ac + db) + ad(bd + ca)= (bc + ad)(ac + bd)
2. (y^2+ab)^2-(a+b)^2*y^2= [ (y^2 + ab) - (a+b)y ] [ (y^2 + ab) + (a+b)y ]= (y - a)(y - b) (y + a)(y + b)
3. (ax+by)^2+(ay-bx)^2= (ax)^2 + 2axby + (by)^2 + (ay)^2 - 2aybx + (bx)^2= (ax)^2 + (ay)^2 + (bx)^2 + (by)^2= (a^2)(x^2 + y^2) + (b^2)(x^2 + y^2)= (a^2 + b^2)(x^2 + y^2)
4. a^n*b^n+b^(n+1)+a^n+b= a^n*b^n + a^n + b^(n+1) + b= (a^n)(b^n + 1) + b(b^n + 1)= (a^n + b)(b^n + 1)
5. (x^2+3x+1)^2+2(x^2+3x+1)-8 Let y = x^2+3x+1 ,= y^2 + 2y - 8= (y - 2)(y + 4)= (x^2+3x+1 - 2)(x^2+3x+1 + 4)= (x^2 + 3x - 1)(x^2 + 3x + 5)