第1个回答 2010-11-25
2A+B
=2(-x²+ax-1)+2x²+3ax-2x-1
=-2x²+2ax-2+2x²+3ax-2x-1
=2x²-2x²+2ax+3ax-2x-1-2
=5ax-2x-3
=(5a-2)x-3
多项式2A+B的值与字母x的取值无关
即5a-2=0
a=2/5
(2x²+ax-y+6)-(2bx²-3x+5y-1)
=2x²+ax-y+6-2bx²+3x-5y+1
=2x²-2bx²+ax+3x-y-5y+6+1
=2(1-b)x²+(a+3)x-6y+7
代数式(2x²+ax-y+6)-(2bx²-3x+5y-1)的值与字母x所取的值无关
即(a+3)=0,2(1-b)=0
a=-3 ,b=1
-1/3 a³-2b²-(1/4 a³-2b²)
=-1/3 a³-2b²-1/4 a³+2b²
=-1/3 a³-1/4 a³+2b²-2b²
=-1/3 a³-1/4 a³
=-(1/3 +1/4) a³
=-7/12*a³
=-7/12*(-3)³
=-7/12*(-27)
=63/4本回答被网友采纳