三分之一（6x^2-1又二分之一+9x)-4(二分之一x^2+x-四分之三),其中x=-2
=2x²-1/2+3x-2x²-4x+3
=-x+5/2
=2+5/2
=9/2
设M=3a^3-10a^2-5, N=-2a^3+5-10a, P=7-5a-2a^2, 求2M+3N-3P的值
2M+3N-3P
=6a³-20a²-10-6a³+15-30a-21+15a+6a²
=-14a²-15a-36
2(x^2y-2xy^2)-4(3x^2y-xy^2)
=2x²y-4xy²-12x²y+4xy²
=-10x²y