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化简再求值(1)(5b-2a)-3(3a-2b),其中b-a=2...

(1)原式=5a-4b;(2)原式=15a2b-5ab2+12ab2-8a2b=7a2b+7ab2,当a=-2,b=3时,原式=84-126=-38;(3)(2x2+ax-y+6)-(2bx2-3x+5y-1)=2x2+ax-y+6-2bx2+3x-5y+1=(2-2b)x2+(a+3)x-6y+7,∵代数式的值与字母x无关,∴2-2b=0,a+3=0,即a=1,b...

2ab+5b²+3a²-2ab =3a²+5b²

∵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.

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

A=4a²+5b B=-3a²-2b 2A-B=8a²+5b+3a²+2b=11a²+7b=44+7=51

请看答案56和过程:

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

=(a-5b)(5a+b)=5a²+ab-25ab-5b²=5a²-24ab-5b²

(2a一5b)一{一3b一2[4a一2(3a-b]} = 2a-5b+3b+2[4a一2(3a-b] = 2a-2b + 2[4a-6a+2b] = 2a-2b + 2[-2a+2b] = 2a-2b - 2[2a-2b] = -(2a-2b) = 2b-2a

2a-3a+2b-4a+5b-6c -5a+7b-6c

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