Why 3rd ODE could be simplified to a 1st ODE?

Verify that the 3rd ODE

$\displaystyle \mu^2\mu'''=\nu (2\mu \mu''-\mu'^2)$

admit two infinitesimal generator

$\displaystyle X_1=\frac{\partial}{\partial x}, X_2=x\frac{\partial}{\partial x}+\mu\frac{\partial}{\partial \mu}.$

And using these symmetry to simplify the above ode to a 1rst order ODE.

I could only verify the vector fields indeed are infinitesimal generators of the 3rd ODE. However, I do not know how to simplify the ODE. Would you help me?

This is Problem 6.3 in

**A practical course in differential equations and mathematical modelling**

by Nail H. Ibragimov,Nailʹ Khaĭrullovich Ibragimov