Sin a +sin 2a +sin 3a +...+sin 36a=0
(sin a+sin 36a)+(sin 2a+sin 35a)+...+(sin18a +sin 19a)=0
2sin (37a/2) *cos (35a/2) +2sin(37a/2) *cos(33a/2)+...+2sin(37a/2) cosa/2=0
2sin(37a/2)*( cos (35a/2)+cos(33a/2)+...+cosa/2 )=0
sin(37a/2)=0 ili cos(35a/2)+cos(33a/2)+cos(31a/2)+cos(29a/2)+...+cosa/2)=0
a=0 (cos(35a/2)+cosa/2)+ (cos(33a/)+cos(3a/2)+...+ =0
2cos(34a/4) *cos(36a/4+2cos(30a/4)*c0s(36a/4)+...=0
2cos(36a/4) *(cos(34a/4)+cos(30a/4)+...)=0
так и дальше смотреть! По-другому не знаю!