### 4.4.4 `fsolve` or `nSolve` with the option `newton_solver`

`newton_solver` is the standard Newton method.
The algorithm starts at an init value *x*_{0}, then we search the
intersection *x*_{1} of the tangent at *x*_{0} to the graph of *f*, with the *x*
axis, the next iteration is done with *x*_{1} instead of *x*_{0}.
The *x*_{i} sequence is defined by

*x*_{0}=*x*_{0}, *x*_{n+1}=*x*_{n}− | | |

If the Newton method converges, it is a quadratic convergence for
roots of multiplicity 1.

Input :

`fsolve((cos(x))=x,x,0,newton_solver)`

Output :

`0.739085133215`