2x²-9x+11=0
（x+1）（2x-11）=0
x=-1或x=11/2是三次方。solve('2*x^3-9*x+11=0') ans =- 3/(2*(11/4 - 67^(1/2)/4)^(1/3)) - (11/4 - 67^(1/2)/4)^(1/3) 3/(4*(11/4 - 67^(1/2)/4)^(1/3)) + (11/4 - 67^(1/2)/4)^(1/3)/2 - (3^(1/2)*(3/(2*(11/4 - 67^(1/2)/4)^(1/3)) - (11/4 - 67^(1/2)/4)^(1/3))*i)/2 3/(4*(11/4 - 67^(1/2)/4)^(1/3)) + (11/4 - 67^(1/2)/4)^(1/3)/2 + (3^(1/2)*(3/(2*(11/4 - 67^(1/2)/4)^(1/3)) - (11/4 - 67^(1/2)/4)^(1/3))*i)/2