Hi all and thanks for the help. I am so angry at myself for having forgotten everything I learned in college about differential equations . I have the following one but I'm stumped at the first hurdle.

$\displaystyle \frac{d^2\theta}{dt^2} - \sin\theta = 0$

Basically I don't know what to do to integrate the sin term wrt t. Do I have to make some kind of small angle assumption (i'd rather not)? This is the same problem as the simple pendulum equation

here but I can't find a really clear solution to it anywhere online.

Any help with this would be fantastic, also if anyone knows of a good undergrad level math book that focuses on differential equations describing physical systems that'd be great.

Thanks all

!

mgri