Question

cos2x = cosx

help?

Answer 1

Do you know the Double Angle fomulas for \(\cos(2x)\)? You can use the version with only cosines in it.

Answer 2

i know that cos2x will be cos^2x -sin^2x thats the one i'm using. Should I use 2cos^2x -1

Answer 3

what are you trying to do with it?

Answer 4

cos2x=cosx

No method to prove the identity could be found.
Not an Identity

Answer 5

cos2x=cosx

For the two functions to be equal, the arguments of each must be equal.
2x=x

Since x contains the variable to solve for, move it to the left-hand side of the equation by subtracting x from both sides.
2x-x=0

Since 2x and -x are like terms, add -x to 2x to get x.
x=0

Answer 6

Yes. Substitute for cos(2x) and you have a quadratic equation. You may be able to factor it.

Answer 7

x = 0 is an obvious solution. There may be others.

Answer 8

thank you

Answer 9

Did you find other solutions?