1.3xy-4xy-(-2xy)

题目

1.3xy-4xy-(-2xy)
2.- 1/3 ab- 1/4 a²+ 1/3 a²-(-2/3ab)
3.(-x+2x²+5)+(4x²-3-6x)
4.(3a²-ab-+7)-(-4a²+2ab+7)

答案

1.3xy-4xy-(-2xy)=-xy+2xy=xy
2.- 1/3 ab- 1/4 a²+ 1/3 a²-(-2/3ab)
=1/3 a²-1/4a²-1/3ab+2/3ab
=1/12a²+1/3ab
3.(-x+2x²+5)+(4x²-3-6x)
=2x²-x+5+4x²-6x-3
=6x²-7x+2
4.(3a²-ab+7)-(-4a²+2ab+7)
=3a²-ab+7+4a²-2ab-7
=7a²-3ab