Resposta :

a) A+B
(5+2x+1) + (+3x-9)

5 +2x +1 +3x -9
2x +3x +5 +1 -9
2x +3x +6 -9
5x -3

b) A-B

 (5+2x+1) - (+3x-9)
5+2x +1 -3x +9
2x -3x +5 -1 +9
2x -3x +5 +9 -1
2x -3x +14 -1
-x+13

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