f[x__]:=(Sqrt Sqrt[-E^(-2 p x) g R (-2-14 p^2-E^(2 p x) Cos[x]+2 E^(2 p x) p^2 Cos[x]+3 E^(2 p x) p Sin[x])])/Sqrt[1+4 p^2]
g = 10
R = 2
p = 0.3
And I want to find a root for:
f[x]^2 == - g R Cos[x]
When I try Solve, I get: "This function cannot be solved with the methods available for Solve", the same for Reduce, and when I try Root: "... is not an univarirate polynomial"
How can I approximate a root of the equation above?