# Exercise 6: Trig functions 
**(15 minutes)**

The quantity theta, or the angle that the beam makes with the *z*-axis,
is calculated by:

$$
\theta = \arctan\left(\frac{p_{T}}{p_{z}}\right)
$$

The units are radians. Define a new column for $\theta$ and plot it as a 
histogram. One more time: don't forget to label the axes!

:::{note}
I'll make your life a little easier: the math function you want is
`atan2(y,x)`, which computes the arctangent of y/x. It's
better to use this function than `atan(y/x)`, because the
`atan2` function correctly handles the case when *x*=0.
:::

:::{figure-md} radians_are_cursed-fig
:align: center

<img src="https://imgs.xkcd.com/comics/radians_are_cursed.png" alt="xkcd radians_are_cursed" width="75%">

<https://xkcd.com/2748/> by Randall Munroe
:::