x^3=x+3
x=(x+3)^(1/3)
f(x)=x-(x+3)^(1/3)
f'(x)=1-1/3*(x+3)^(-2/3)
X(n+1)=Xn-f(xn)/f'(xn)
x0=0
x1=1.7175
x2=1.6717
x3=1.6717
x4=1.6717
x5=1.6717