x^3+3x-4
=x^3 + (x^2 - x^2) + (4 x - x) - 4
=x^3 + x^2 + 4 x - x^2 - x - 4
= (x^2 + x + 4) x - (x^2 + x + 4)
= (x^2 + x + 4)(x -1)=0
x^2+x+4={(x+0.5)^2+3.75}不能等于o 所以x=1
x^3+3x-4
=x^3 + (x^2 - x^2) + (4 x - x) - 4
=x^3 + x^2 + 4 x - x^2 - x - 4
= (x^2 + x + 4) x - (x^2 + x + 4)
= (x^2 + x + 4)(x -1)=0
x^2+x+4={(x+0.5)^2+3.75}不能等于o 所以x=1