a) 5x^5-x^4+3x^2+x+x^4+3x^2-2x+1=5x^5+6x^2-x+1
5x^5-x^4+3x^2+x-x^4-3x^2+2x-1=5x^5-2x^4+6x^2+3x-1
b) 12a²-6b-7c+d+3a²+2b+4c-d=12a²-4b-3c
12a²-6b-7c+d-3a²-2b-4c+d=9a²-8b-11c+2d
a) 5x^5-x^4+3x^2+x+x^4+3x^2-2x+1=5x^5+6x^2-x+1
5x^5-x^4+3x^2+x-x^4-3x^2+2x-1=5x^5-2x^4+6x^2+3x-1
b) 12a²-6b-7c+d+3a²+2b+4c-d=12a²-4b-3c
12a²-6b-7c+d-3a²-2b-4c+d=9a²-8b-11c+2d