Having problems with working out surds from radians. Does anyone now the whereabouts on the net where there is an extensive chart? At the moment i am struggling with cos(5*pi/6).

Cheers in advance

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- Aug 8th 2006, 07:58 AMkendonRadians and surds
Having problems with working out surds from radians. Does anyone now the whereabouts on the net where there is an extensive chart? At the moment i am struggling with cos(5*pi/6).

Cheers in advance - Aug 8th 2006, 08:04 AMThePerfectHackerQuote:

Originally Posted by**kendon**

Your problem is this, you need a way to express trigonometric functions of certain angles in radical form. I remember when I was in 11th grade my cl*** was going insane with this so I have a trick which you can do.

For example,

$\displaystyle \cos \frac{5\pi}{6}=-0.86602541$

Now, if you end up with a long decimal square,

$\displaystyle (-0.86602541)^2=.75$

But,

$\displaystyle .75=\frac{3}{4}$

Now, that the square root back.

$\displaystyle \sqrt{\frac{3}{4}}=\frac{\sqrt{3}}{2}$

**Important**. When you square the sign always goes away. Therefore, if you had a sign in the beginning (and you did) when you need to attach a sign here. - Aug 8th 2006, 08:16 AMCaptainBlackQuote:

Originally Posted by**kendon**

of half of an equilateral triangle), and the cosine function is even so

$\displaystyle \cos(5 \pi/6)=\cos(-\pi/6)=\cos(\pi/6)=\sqrt{3}/2$

RonL