编辑本段例题
例1:先去括号,再合并同类项 (1) 5a-(2a-4b) ; (2) 2x2+3(2x-x2) (3) 4+7(2x+8x) 解:(1)5a-(2a-4b) =5a-2a+4b =3a+4b (2)2x2+3(2x-x2) =2x2+6x-3x2 =-x2+6x (3)4+7(2x+8x) =4+14x+56x =4+70x 例题:先去括号,再合并同类项 a-(2a-b)-(a+2b) 解:=a-2a+b-a-2b =-2a-b -(x2-y2)+(-4x2-1)-(x2+y2) 解:=-x2+y2-x8-1-x2-y2 =-12x-1 (x2-y2)-4(2x2-3y) 解:=x2-y2-16x+12y =-14x+10y 2(5a2-2ab)-3(3a2+4ab-b2) 解:=20a-4ab-18a-12ab+6b =2a-16ab+6b 计算:4xy-3x2y-{3x2y+xy2- [2xy2-4x2y+(x2y-2xy2)]} 化简 (a2-b2)-2(3a2-2b2) (8x-3y)-(4x+3y-z)+2z 2m-3n+[5m-(3m-n)] -(2a-b)-{b-[a-(2a-b)]} 已知m-n=3, 求4(m-n)-3m+3n+5的值 a+(b+c)=a+b+c或a+(b-c)=a+b-c a-(b-c)=a-b+c或a-(b+c)=a-b-c