G gkagawa New member Joined Mar 28, 2010 Messages 9 Nov 11, 2010 #1 Prove cosx = cos2x I tried using the double angle identity for the RHS to get this: = cos^2x - sin^2x = (cosx - sinx) (cosx + sinx) What next?
Prove cosx = cos2x I tried using the double angle identity for the RHS to get this: = cos^2x - sin^2x = (cosx - sinx) (cosx + sinx) What next?
G galactus Super Moderator Staff member Joined Sep 28, 2005 Messages 7,203 Nov 11, 2010 #2 \(\displaystyle cos(x)=cos(2x)\) is not an identity. Are you solving for x?.
D Deleted member 4993 Guest Nov 11, 2010 #3 gkagawa said: Prove cosx = cos2x I tried using the double angle identity for the RHS to get this: = cos^2x - sin^2x = (cosx - sinx) (cosx + sinx) What next? Click to expand... In general "cos(x) = cos(2x)" is not an identity. This equation is true only for certain values of "x". So you cannot "prove" the statement.....
gkagawa said: Prove cosx = cos2x I tried using the double angle identity for the RHS to get this: = cos^2x - sin^2x = (cosx - sinx) (cosx + sinx) What next? Click to expand... In general "cos(x) = cos(2x)" is not an identity. This equation is true only for certain values of "x". So you cannot "prove" the statement.....
