3m2n+6mn2-mn2-m2n
-3x2y+5xy2-6xy2+4-7x2y-9
xy2+(-3x2y)+4xy2+(-5x2y),
(3x-5y)-(6x+7y)+(9x-2y)
2a-[3b-5a-(3a-5b)] (6m2n-5mn2)-6(m2n-mn2)
m2+(-mn)-n2+(-m2)-(-0.5n2)
2(4an+2-an)-3an+(an+1-2an+1)-(8an+2+3an)
(x-y)2-(x-y)2-[(x-y)2-(x-y)2]
a-(a-3b+4c)+3(-c+2b)
(3x2-2xy+7)-(-4x2+5xy+6)
2x2-{-3x+6+[4x2-(2x2-3x+2)]}
a>0,
