Expert: Paul Klarreich - 12/5/2008

Question
thank you for your help before, I really appreciated it :)

I rewrote the other question that you had a hard time reading:

sin x * cos(x/2) - 1 = cos x

I'm having trouble with this one, I've been trying to figure it out, but I can't seem to get to cos x.

I know 1 = sin^2x + cos^2x, and the cos(x/2) is the half angle formula for cos. I just need help getting it to equal cosine.

thanks.

Answer
Questioner:   Tyler
Category:  Advanced Math
Private:  No
 
Subject:  Trigonometric Identities
Question:  thank you for your help before, I really appreciated it :)

I rewrote the other question that you had a hard time reading:

sin x * cos(x/2) - 1 = cos x

I'm having trouble with this one, I've been trying to figure it out, but I can't seem to get to cos x.

I know 1 = sin^2x + cos^2x, and the cos(x/2) is the half angle formula for cos. I just need help getting it to equal cosine.

thanks.

.....................
Hi, Tyler,

There is a good reason you can't prove this identity:  IT ISN'T TRUE.  (try graphing the left and right sides.)

P.S.  Tell your friend 'Dave' that I'll answer his questions as soon as I am convinced he is a real person.