Uh oh! Wolfram|Alpha doesn't run without JavaScript.
Please enable JavaScript. If you don't know how, you can find instructions
here
.
Once you've done that, refresh this page to start using Wolfram|Alpha.
90 * (1 - (ArcCos[ 1/12 ] / (Pi / 2)))
90 * (1 - (ArcCos[ 1/12 ] / (Pi / 2)))
Natural Language
Math Input
Extended Keyboard