Question 255505
multiply x^9 by the three terms
x^9*x^9+x^9*x^8-x^9*x^7
multiply x^8 by the three terms
x^8*x^9+x^8*x^8-x^*8*x^7


x^9*x^9+x^9*x^8-x^9*x^7+x^8*x^9+x^8*x^8-x^*8*x^7
now combine like terms
x^18+x^17-x^16+x^17+x^16-x^15
x^18+2x^17-x^15 or 
factored x^15(x^3+2x^2-1)