cos 40+cos 80+cos 160+cos 240 = ?...want a step-by-step answer...40,80,160,240 are degrees...

Question

shamil98 · Answer

what do you want to do with it just simplify?

anonymous · Answer

ya..

shamil98 · Answer

Okay.
Evaluate cos at those respective degrees and then add them up, right?

shamil98 · Answer

Wolframalpha gave me -1/2

kc_kennylau · Answer

I got -0.5 also at W/A but idk y...

anonymous · Answer

answer..is -0.5,but we can't do it by evaluation,I mean we can't remember those values in exam.

anonymous · Answer

I want a step-by-step answer

kc_kennylau · Answer

anonymous · Answer

this one's so long....

kc_kennylau · Answer

lolz

anonymous · Answer

A minor point, but an important one: unless you state that those numbers are degrees, then they're assumed to be radians. Did you mean degrees?

anonymous · Answer

@dkco   ,sorry for not mentioning,those are degrees