Question 912352
how to factor 
x^13-15x^9-16x^5?
=x^5(x^8-15x^4-16)
=x^5(x^4+1)(x^4-16)
=x^5(x^4+1)(x^2+4)(x^2-4)
=x^5(x^4+1)(x^2+4)(x+2)(x-2)