fsolve or nSolve with the option newton_solver

### 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 x0, then we search the intersection x1 of the tangent at x0 to the graph of f, with the x axis, the next iteration is done with x1 instead of x0. The xi sequence is defined by

x0=x0, xn+1=xn− |
f(xn)
f′(xn)

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`