Prove the trig identity: cos(-x)+cos(pi-x)=cos(pi+x) + cos(x)

Expert Answers
crmhaske eNotes educator| Certified Educator

`cos(-x) = cos(x)`

`cos(pi-x)=-cos(x)`

`cos(pi+x)=-cos(x)`

Therefore:

`cos(x)-cos(x)=-cos(x)+cos(x)`

`0=0`

Since the left side equals the right side, the original equation is true.