### 8.4.4 fsolve or nSolve with the option newton_solver

newton_solver is the standard Newton method.
The algorithm starts at an initial 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