(trig-functions-c)=
# Exercise 7: Trigonometric functions 
**(15 minutes)**

Revise AnalyzeVariables.C to include a histogram of **{ref}`theta <treeviewer-expressions>`**.

:::{note}
I'll make your life a little easier: the math function you want is
`TMath::ATan2(y,x)`, which computes the arctangent of y/x. It's
better to use this function than `TMath::ATan(y/x)`, because the
`ATan2` function correctly handles the case when *x*=0.
:::

:::{figure-md} los_alamos-fig
:class: align-center

<img src="https://imgs.xkcd.com/comics/los_alamos.png" alt="xkcd los_alamos" width="80%">

<https://xkcd.com/809/> by Randall Munroe
:::