How to calculate triangle's angle

Question

Following this image, I have C1, C2 and H values. How to calculate the angle?

Answer 1

Let the angle you're looking for, be $\theta$. Have you come across trigonometry yet (especially inverse trigonometric functions)? You're looking for $\theta$ such that $$\tan\theta = \frac{C_2}{C_1}$$ $$\implies \theta = \arctan\frac{C_2}{C_1}$$ where $\arctan$ is just $\tan^{-1}(x) \in [-\frac{\pi}{2},\frac{\pi}{2}]$, i.e. the inverse function of $f(x) = \tan x$.