hi-prove-this-cos-pi-10-cos-4pi-10-cos-6pi-10-cos-9pi-10-0-by-the-easiest-possible-way-

Question Number 139409 by henderson last updated on 26/Apr/21

hi!

prove this :

c o s \frac{π}{10} + c o s \frac{4 π}{10} + c o s \frac{6 π}{10} + c o s \frac{9 π}{10} = 0 .

(by the easiest possible way \dots!)

Answered by mr W last updated on 26/Apr/21

\cos α + \cos (π - α) = 0

\cos \frac{π}{10} + \cos \frac{9 π}{10} = 0

\cos \frac{4 π}{10} + \cos \frac{6 π}{10} = 0

\dots . = 0

Commented by henderson last updated on 26/Apr/21

waoh! thank u very much, sir w!