(2x+5y)+(3x-2y)
=5x+3y
(3x3 +3x2 -4x+5)+(x3 -2x2+x-4)
=4x3+x2 -3x+1
(7x2 -x-4)+(x2 -2x-3)+(-2x2 +3x+5)
=6x2 -2
(x3+5x2 -2x)+(x3+3x-6)+(-2x2+x-2)
=2x2+3x2+2x-8
(x3+3x2+5x-4)-(3x3 -8x2 -5x+6)
=-2x3+11x2+10x-10