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.
NSolve[{2(Cos[2x])^2 + Cos[2x] - 1 == 0, 0 <= x <= 2Pi}, x]
NSolve[{2(Cos[2x])^2 + Cos[2x] - 1 == 0, 0 <= x <= 2Pi}, x]
Natural Language
Math Input
Extended Keyboard