Add Newton and secant method in the derivative lecturue

[qzhu2017]

Can be used to solve the root of single variable function f(x)=0.
f(x) = exp(x)*lnx - x**2

find the bond length of NaCl
V(r) = -e^2/r + ae^{-r/p}
a = 1.0910^3 eV
p = 0.330
e2 = 14.4
Tao Pang, pp 37