I think you are referring to a wonderful theorem, "Abel's Theorem".

Consider,

Where, are some functions defined on an open interval.

Assume,

are two function that satisfy the differencial equation throughtout this open interval.

That means,

Now,

Now the Wronskian is differenciable on this open interval and,

The trick is to multiply the system of differencial equations by certain functions that will transform them into the Wronskian form.

Multiply the first equation by :

Multiply the second equation by :

Add these equations, Hacker style,

Thus,

This is a first order linear differencial equation which can be solved easily if is countinous throughout the interval.

I can solve it for thee but I believe thou can complete it thyself.