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化简再求值(1)(5b-2a)-3(3a-2b),其中b-a=2...

∵A=4a2+5b,B=-3a2-2b,∴2A-B=2(4a2+5b)-(-3a2-2b),=8a2+10b+3a2+2b,=11a2+12b,把a=-2,b=1代入,原式=11×(-2)2+12×1=56.

分解因式 见图

2ab+5b²+3a²-2ab =3a²+5b²

由题意得: 原式可化为3-2b-2a+5b+1-8b-3a-1 =-5a-5b+3 当a=2/3,b=-1/4时 原式=-5*2/3+5*1/4+3=11/12

1/a+1/2b=3 2a-5ab+4b/4ab-3a-6b 分数式的分子分母上下同除以4ab商不变.(易知4ab不为0) =(1/2b-5/4+1/a)/(1-3/4b-3/2a) =(1/2b+1/a-5/4)/(1-3/2(1/a+1/2b)) 代入已知 1/a+1/2b=3 =(3-5/4)/(1-(3/2*3)) =(7/4)/1-9/2) =7/4/(-7/2) =-1/2

请看答案56和过程:

∵A=4a2+5b,B=3a2-2b,∴2A-B=8a2+10b-3a2+2b=5a2+12b,把a=-2,b=1代入得:原式=20+12=32.

即6a²+mab-10b²=(3a-2b)(2a+5b) (3a-2b)(2a+5b) =3a(2a+5b)-2b(2a+5b) =6a²+15ab-4ab-10b² =6a²+11ab-10b² =6a²+mab-10b² 所以m=11

∵(4a+1)2+|2b-a-34|=0,∴4a+1=0.2b-a-34=0,解得a=-14,b=14,∴4(3a-5b)-3(5a-7b+1)+(2a+7b-1),=-a+8b-4,=-(-14)+8×14-4=-134.

∵(4a+1) 2 +|2b-a- 3 4 |=0,∴4a+1=0.2b-a- 3 4 =0,解得a=- 1 4 ,b= 1 4 ,∴4(3a-5b)-3(5a-7b+1)+(2a+7b-1),=-a+8b-4,=-(- 1 4 )+8× 1 4 -4=-1 3 4 .

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