# The Addition and subtraction Formulas

• March 16th 2010, 05:38 PM
purplec16
If $sin \alpha = \frac{-5}{13}$ and tan is less than 0, find the exact value of $sin (\alpha-\frac{\pi}{3})$

How do you find the exact value do you use the Sine of differences or do you use the cofunction identities for any real number t?
• March 16th 2010, 06:31 PM
harish21
Quote:

Originally Posted by purplec16
If $sin \alpha = \frac{-5}{13}$ and tan is less than 0, find the exact value of $sin (\alpha-\frac{\pi}{3})$

How do you find the exact value do you use the Sine of differences or do you use the cofunction identities for any real number t?

$sin(A-B) = sinA*cos B - cosA*sinB$

Use your given values of A and B in the above equation and you should have your answer.

Keep in mind that :

$\cos A = \sqrt{1-sin^{2}A}$