SOLUTION: i got 2n(pi) +or- pi/3 and 2n(pi) +or- pi as solutions for the equation cos x+cos 2x=0. but the book's answer says (2n+1)pi/3. I would like to know how could that be.

Question 970967: i got 2n(pi) +or- pi/3 and 2n(pi) +or- pi as solutions for the equation cos x+cos 2x=0. but the book's answer says (2n+1)pi/3. I would like to know how could that be.
Answer by josgarithmetic(39618) (Show Source): You can put this solution on YOUR website!

or
Notice where x points to on the unit circle for these cosines.
pi/3, 3pi/3, 5pi/3, and then as you continue to rotate in increments of to maintain those, you see difference of 2pi/3 each time.
... next value for x would be 7pi/3.

...as you keep on thinking on this, notice that x will be ODD increments of pi/3. Now observe that your numerator for x IS AN ODD NUMBER.
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