Math Help - Critical equation

1. Critical equation

solve in R this equation :

2. Originally Posted by dhiab
solve in R this equation :
Hint: $\cos{(2x)} = 2\cos^2{x} - 1$ and $\cos{(3x)} = 4\cos^3{x} - 3\cos{x}$.

Substitute these values appropriately and you should be able to solve the equation.