How solve this trigo system ?

[Gerson W. Barbosa]

(09-18-2017 10:45 AM)ggauny@live.fr Wrote:  Thank Gerson,

You say first 2 roots, so there are others ?

The vector returned by PROOT contains four roots.

The other two appear to be

'(1-3*√3)/4' and '(1+3*√3)/4'.

You might want to solve the quartic equation symbolically to check the results. I fear I cannot do that by hand :-)

Notice those are solutions for cos(x). The solutions for x are obviously the arccosine of those values.

W|A lists them all:

http://m.wolframalpha.com/input/?i=solve...2F64+%3D+0