Re: Bernoulli equation
The Bernoulli equation takes the form
\[\frac{dy}{dx} + p(x) y = q(x) y^n\]
In your case \[p(x) = -\frac{1}{x}\], \[q(x) = \frac{\cos x}{x^3}\], \[n=4\].
You would start by creating a new variable \[v=y^{1-n}=y^{-3}\],
and follow the formulation given here
Bernoulli Differential Equation -- from Wolfram MathWorld
Following the procedure, I am getting
\[y = \frac{x}{\sqrt[3]{-3 \sin x + C}}\]
where \[C\] is a constant. I did not check the result by plugging it back into
the original differential equation yet. Why don't you go through the procedure to see what you get.
I hope this points you in the right direction.
Best regards,
v_c