what exactly don't you understand?, it's stright forward, you substitute and get a first order ODE.1. Find the general solution of each differential equation using the substitution given.

x(d^2 y)/(d x^2) – 2 dy/dx + x = 0; dy/dx = v

2.

now use the chain rule:

thus:

now substitute the resulting expressions in the DE:

multiply the equationn by:

and you'll get a regular ODE...