Question 397432

{{{cos(x) = -0.2108}}}

arccos always returns value on interval [0, π]

x = arccos(-0.2108), 2π - arccos(-0.2108)
x = 1.783189604,   or... 4.499995704
x = 1.78,...or... 4.50

Check: 

cos(1.7831896041) = −0.2108, 
cos(4.499995704) = −0.2108