trigonometric multiple angle formula

Apr 2018
3
0
London
Hi could I get Help with this question really struggling I need to use angle formula to show cos^2x=1/2 (cos2x-1).
 

SlipEternal

MHF Helper
Nov 2010
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Which "angle formula" are you supposed to use? Are you talking about the double angle formula for cosine?

\(\displaystyle \cos(2x) = 2\cos^2 x -1\)

Is that the "angle formula" you are referring to? If it is, then add 1 to both sides. Then divide both sides by 2.
 
Apr 2018
3
0
London
I haven't been given one I've been told to use one of the multiple angle formula as to which one to use I'm not quite sure
 

SlipEternal

MHF Helper
Nov 2010
3,728
1,571
How about:
$\cos(\alpha + \beta) = \cos \alpha \cos \beta - \sin \alpha \sin \beta$

Let $\alpha = x$ and $\beta=x$. See what you get on the left and right sides.
 

Plato

MHF Helper
Aug 2006
22,506
8,663
Hi could I get Help with this question really struggling I need to use angle formula to show cos^2x=1/2 (cos2x-1).
The question is written incorrectly
It should be $\cos^2(x)=(1/2) (\cos(2x)\large\color{red}+1)$
 
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Apr 2018
3
0
London
Yeah I thought so I asked my teacher and he said he made a mistake with the question and it was incorrect thanks for pointing it out