a) (−4x3−13x2+2x5)+(13x2+2x3−12x−1)
= −4x3−13x2+2x5+13x2+2x3−12x−1=2x5−2x3−12x−1
b) (12x6−11x2+3x3+9)−(13x6+2x3−11x2−11x)
= 12x6−11x2+3x3+9−13x6−2x3+11x2+11x=−x6+x3+11x+9
c) (8x3−x2+1)(x2−1)=8x5−8x3−x4+x2+x2−1=8x5−8x3−x4+2x2−1
d) (8x3+6x2+3x+1)/(2x+1)=4x2+x+1
