可能不太够
(x+5y)-(3y-4x)=x+5y-3y+4x
1/2(x6^2-y)+1/3(x-y^2)+(x^2）（^为平方号）
10a+6b-7a+3b-10a+10b+12a+8b
4xy-2y+3x-xy
(3x-5y)-(6x+7y)+(9x-2y)
2a-[3b-5a-(3a-5b)]
(6m2n-5mn2)-6(m2n-mn2)
(5x-4y-3xy)-(8x-y+2xy)
a-(a-3b+4c)+3(-c+2b)
7x2-7xy+1
6-5b-(3a-2b)-(1-6b)
(5x-4y-3xy)-(8x-y+2xy)
(3x2-4xy+2y2)+(x2+2xy-5y2)
(x-y)2-(x-y)2-[(x-y)2-(x-y)2]
(2k-1)x2-(2k+1)x+3
2(x-2)-3x-2
2y-3y+1-6y
3b-6c+4c-3a+4b
2a-5b+4c-7a+5a+5b-4c
4a+6c+7a-6a+7b-3c-6b
5b+2c-7b+4z-3z
3b+3c-6a+8b-7c-2a
3c-7b+5z-7b+4a-6n+8b-3v+9n-7v
3x2-1-2x-5+3x-x2
-0.8a2b-6ab-1.2a2b+5ab+a2b
6x2y+2xy-3x2y2-7x-5yx-4y2x2-6x2y
4x2y-8xy2+7-4x2y+12xy2-4；
a2-2ab+b2+2a2+2ab - b2．
-4x2y-8xy2+2x2y-3xy2；
3x2-1-2x-5+3x-x2；
　-0.8a2b-6ab-1.2a2b+5ab+a2b；
5yx-3x2y-7xy2+6xy-12xy+7xy2+8x2y． 可能不太够
(x+5y)-(3y-4x)=x+5y-3y+4x
1/2(x6^2-y)+1/3(x-y^2)+(x^2）（^为平方号）
10a+6b-7a+3b-10a+10b+12a+8b
4xy-2y+3x-xy
(3x-5y)-(6x+7y)+(9x-2y)
2a-[3b-5a-(3a-5b)]
(6m2n-5mn2)-6(m2n-mn2)
(5x-4y-3xy)-(8x-y+2xy)
a-(a-3b+4c)+3(-c+2b)
7x2-7xy+1
6-5b-(3a-2b)-(1-6b)
(5x-4y-3xy)-(8x-y+2xy)
(3x2-4xy+2y2)+(x2+2xy-5y2)
(x-y)2-(x-y)2-[(x-y)2-(x-y)2]
(2k-1)x2-(2k+1)x+3
2(x-2)-3x-2
2y-3y+1-6y
3b-6c+4c-3a+4b
2a-5b+4c-7a+5a+5b-4c
4a+6c+7a-6a+7b-3c-6b
5b+2c-7b+4z-3z
3b+3c-6a+8b-7c-2a
3c-7b+5z-7b+4a-6n+8b-3v+9n-7v
3x2-1-2x-5+3x-x2
-0.8a2b-6ab-1.2a2b+5ab+a2b
6x2y+2xy-3x2y2-7x-5yx-4y2x2-6x2y
4x2y-8xy2+7-4x2y+12xy2-4；
a2-2ab+b2+2a2+2ab - b2．
-4x2y-8xy2+2x2y-3xy2；
3x2-1-2x-5+3x-x2；
　-0.8a2b-6ab-1.2a2b+5ab+a2b；
5yx-3x2y-7xy2+6xy-12xy+7xy2+8x2y．