# Re: exact value of SIN 15 COS 15 TAN 15?

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Posted by T.Gracken on June 08, 2002 at 16:06:29:

In Reply to: exact value of SIN 15 COS 15 TAN 15? posted by Matthew on June 08, 2002 at 15:59:26:

: How does one find the exact value of sin 15 cos 15 and tan 15....and could some body please show me a solution for at least one of those questions ?
: thank you graciously if you can provide an answer

There are several ways you can determine the values. The one that comes first to me is to use the difference of angles identities.

I'm going to assume you mean 15 degrees.

example: since you know the exact values for sine and cosine when the angle measure is 30 degrees and 45 degrees, and you know 45 - 30 = 15, rewrite the angle measure as a difference.

sin(15deg.) = sin(45o - 30o)

and sin(u-v)=sin(u)cos(v)-cos(u)sin(v)

see if that's enough for you...

another common identity to use here would be one of the half-angle identities.

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