hi 

for solving equations you can use ode or dsolve commands in matlab & use plot & ezplot for plotting

This is a good practical question.

A good paper on solving and plotting second order nonlinear differential equations is

H.N. Hassan, M.A. El-Tawil, A new technique of using homotopy analysis method for second order nonlinear differential equations, Applied Math. and Computation 219, 2012, 708-728:

http://www.academia.edu/4385978/A_new_technique_of_using_homotopy_analysis_method_for_second_order_nonlinear_differential_equations

The authors of the paper appear to be using Matlab for the plots but do not give their Matlab scripts in the paper.    For related papers and suggestions, see

Professor Hany N. Hassan:

https://www.researchgate.net/profile/Hany_Hassan3

hi

Using the code from Chris Taylor's answer as below:

k = 1;

f = @(t,x) [x(2); -k * x(2) - x(1)^3 + 9.8 * cos(t)];

tspan = [0, 10];

xinit = [0, 0];

[t, y] = ode45(f, tspan, xinit);

gives you the values x and y as functions of t from 0 to 10, stored in the first and second columns of y respectively. Therefore you can plot y(x) by simply calling

plot(y(:,2),y(:,1));

hi 

for solving equations you can use ode or dsolve commands in matlab & use plot & ezplot for plotting

Visit the website