(x-2)(x的2次方-6x-9)-x(-2x-7) 其中x=2分之1
=(x-2)(x的2次方-6x-9)-x(-2x-7)
=x^3-6x^2-9x-2x^2+12x+18+2x^2+7x
=x^3-6x^2+10x+18
其中x=2分之1
上式=(1/2)^3-6*(1/2)^2+10*(1/2)+18
=1/8 - 3/2 +5+18
=21又5/8