Finding the intersection of a line and standard wave function Let's say I have two functions $f(x)=5\cos(x)$ and $g(x)=4$.
The line lies in between the range of the wave function so there will be two intersections for each period of the wave.
I want to find where on the $x$-axis those intersections will occur for a single period. Without resorting to numerical methods to approximate the roots and just using a plain scientific calculator, I'm trying to find both of them.
Setting both functions to equal each other yields me the first intersection, how do I get the next one in the same period?
$$\begin{array}{l}5\cos(x) = 4\\
\cos(x) = 0.8\\
x = \arccos(0.8)\\
x = 0.6435
\end{array}$$


Use $\cos(x) = \cos (2\pi - x) $ property.
