First Order ODE/x dy = (y + x^2 + 9 y^2) dx

Theorem
The first order ODE:
 * $(1): \quad x \, \mathrm d y = \left({y + x^2 + 9 y^2}\right) \mathrm d x$

has the solution:
 * $\arctan \left({\dfrac {3 y} x}\right) = 3 x + C$