$f(x)=-x^3-2x^2-4x-25$ this is the function, and I found the derivative $f' (x)=-3x^2-4x-4$, and put it into Newton's method. I let the first term to be -4, and i got
$x_(n+1)=-4+ 23/36 = -3.63....$
but from the website it sats the first term is -4.06...... it cant be. Everything is right. what is the problem?
from wolframalpha the actual answer is about 3.19
On
If you give the website input complete with multiplications signs,
f(x) : -x^3-2*x^2-4*x-25
f'(x) : -3*x^2-4*x-4
then the expression parser gets the correct function and convergence in 7 steps.
The web page is incorrect and you are correct. After five iterations I get the value $-3.19597980081$ on my TI-Nspire CX. I also get the first iteration value $\frac{-121}{36}\approx -3.361111111111$ (you made a mistake in the decimal approximation).