well, it's all about chain rule! looking at as a function of and each of and as functions of and
applying the chain rule we'll get: and now apply the chain rule again, but
this time for and to get: and finally:
plugging these three in the equation your problem has given us, will give you:
which obviously has the general solution which, in terms of becomes:
for the required specific function, first see that:
we'd like to have i.e.
we also have this condition that which gives us:
solving the system of equations (1) and (2) gives us and where is a constant.thus
by the specific solution is