x^4+6x^2+8
=(x^2+2)(x^2+4)
3a^2-8a+4
=(a-2)(3a-2)
5a^2b^2+23ab-10
=(ab+5)(5ab-2)
x^2y^2-5x^2y-6x^2
=x^2(y^2-5y-6)
=x^2(y+1)(y-6)
x^4-3x^3-28x^2
=x^2(x^2-3x-28)
=x^2(x+4)(x-7)
3a^2b^2-17ab+10
=(ab-5)(3ab-2)
-a^3-4a^2+12a
=-a(a^2+4a-12)
=-a(a+6)(a-2)
x^2-3xy+2y^2
=(x-y)(x-2y)