-2a-b+c;(2)-(x-y)+(xy-1) =-x-y+xy-1. (3)(y-x) 4.化简:(1)(2x-3y)+(5x+4y); (2)(8a-7b)-(4a-5b); (3)a-(2a+b)+2(a-2b); (4)3(5x+4)-(3x-5); (5)(8x-3y)-(4x+3y-z)+2z;(6)-5x ___(a-b)___(c+d)=c+d-a+b2.已知x+y=2,则x+y+3= ,5-x-y= 3.去括号:(1)a+3(2b+c-d); (2)3x-2(3y+2z). (3)3a+4b-(2b+4a); (4)(2x-3y)-3(4x-2y). 4.化简:(1)2a-3b+[4a-(3a-b)]; (2)3b-2c-[-4a+(c+3b)]+c. A.x+2;B.x-12y+2; C.-5x+12y+2; D.2-5x. 课时去括号(1) 1.下列各式中,与a-b-c 的值不相等的是 A.a-(b+c)B.a-(b-c) C.(a-b)+(-c) A.-2p-qB.-2p+q C.2p-q D.2p+q 3.下列去括号中,正确的是 -2x-1C.2y 4.去括号:a+(b-c)= 5.判断题.(1)x-(y-z)=x-y-z 6.去括号:-(2m-3); n-3(4-2m); 7.先去括号,再合并同类项:-2n-(3n-1); a-(5a-3b)+(2b-a); -3(2s-5)+6s; 1-(2a-1)-(3a+3); 3(-ab+2a)-(3a-b); 14(abc-2a)+3(6a-2abc). A.a+b+cB.a-b+c C.-a+b-c D.a-b-c A.6B.-2 C.2 -6 D.6-2 10.先去括号,再合并同类项: 6a ab);2(2a-b)-[4b-(-2a+b)] 9a -t-3)-2]+(2t -3t+1).11.对a 随意取几个值,并求出代数式25+3a-{11a-[a-10-7(1-a)]}的值,你能从 中发现什么?试解释其中的原因.