Finding exact values using the sum and difference identity

**elieh** · July 3rd 2011, 12:48 AM

How can I find the exact value of $cos\frac{\pi}{12}$ using the sum and difference identity?

I'm guessing I'd have to split the fraction up, into 2 parts, but I'm not sure on how to proceed.

Help appreciated.

**e^(i*pi)** · July 3rd 2011, 01:53 AM

$\cos \left(\dfrac{\pi}{12}\right) = \cos \left(\dfrac{\pi}{4} - \dfrac{\pi}{6}\right)$

**Soroban** · July 3rd 2011, 03:50 AM

Another way . . .

$\frac{\pi}{12} \;=\;\frac{4\pi}{12} - \frac{3\pi}{12} \;=\;\frac{\pi}{3} - \frac{\pi}{4}$

**waqarhaider** · July 3rd 2011, 04:41 AM

you can also use the identity cos^2(x/2) = (1+cosx)/2

by taking (pie)/12 = [pie/6]/2

**skeeter** · July 3rd 2011, 07:38 AM

Originally Posted by waqarhaider

you can also use the identity cos^2(x/2) = (1+cosx)/2

by taking (pie)/12 = [pie/6]/2

this is pi ...

this is pie ...

... hungry?

Thread: Finding exact values using the sum and difference identity

LinkBack

Thread Tools

Display

Finding exact values using the sum and difference identity

Re: Finding exact values using the sum and difference identity

Re: Finding exact values using the sum and difference identity

Re: Finding exact values using the sum and difference identity

Re: Finding exact values using the sum and difference identity

Similar Math Help Forum Discussions

Help finding the exact values of sin, sec, and tan

Finding exact values

Finding the Exact value of a tangent using sum and difference

[SOLVED] exact answer using trigonometric difference identity

Finding Exact Values

Search Tags