I have an angle theta given by
Kx = (2/Sqrt) ArcSin[Sqrt[3/10]]; Ky = (2/3) (ArcCos[(1/5) Sqrt[7/10]] - Pi); theta = Cos[ArcTan[Kx, Ky]];
This evaluates, by use of
N[theta] to give 0.5.
However I can't seem to get mathematica (by use of
TrigExpand etc.) to work this out exactly (i.e. not numerically) to give me
Any suggestions on how to achieve this? Although it's not so important for the above example, I will have other situations where the answer may actually be
Sqrt etc. so I don't want to lose that exactness to numerical approximations.