(5x+2x²-3-4x³)-(-x+3x³-x²)其中x=2(5x+2x²-3-4x³)-(-x+3x³-x²)=5x+2x²-3-4x³+x-3x³+x²=-7x³+3x²+6x-3当x=2时,有：-7x³+3x²+6x-3...