计算
(1)-2²÷3分之4-[2²-(1-2分之1×3分之1)]×12
=-4×3/4-(4-1+1/6)×12
=-3-36-2
=-41;
(2)(-3)³×1又4分之1×[-5+(-2)³×8分之3]-(-1)的2008次方×(-1)的2009次方
=-27×(5/4)×(-5-3)-1×(-1)
=270+1
=271;
(3)-2分之1×(-4)²+(-3分之2)×3²
=-1/2×16-2/3×9
=-8-6
=-14;
2.化简求值
5(2x²y-3x)-2(4x-3x²y),其中x=2分之1,y=-1
=10x²y-15x-8x+6x²y
=16x²y-23x
=16×1/4×(-1)-23×(1/2)
=-4-23/2
=-31/2;
3.已知A=x-x²+1,B=x²-1+3x,求A-2B的值.
A-2B=x-x²+1-2x²+2-6x=-3x²-5x+3;
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