Help, conics deriving an equation (1 Viewer)

Praer · Feb 20, 2013

Help, Trig

How does cos(x) - 1 turn into -2sin^2(x/2)
Tnx

Sy123 · Feb 20, 2013

Re: Help, Trig

Praer said:
How does cos(x) - 1 turn into -2sin^2(x/2)
Tnx

Well we know the formula:

$\cos 2\theta = 1-2\sin^2 \theta$

Substiute in theta = x/2

$\cos x = 1-2\sin^2 \frac{x}{2}$

Then put this into the original expression:

$\cos x - 1 = 1-2\sin^2 \frac{x}{2} - 1 = -2\sin^2 \frac{x}{2}$

Praer · Feb 20, 2013

Thanks boss!

Nws m8 · Feb 20, 2013

Why is this in mx2 thread ? :S

Help, conics deriving an equation (1 Viewer)

Praer

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Sy123

This too shall pass

Praer

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Nws m8

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