Double and half angles

Question

Given  and  is in quadrant III, find the exact value of .

 = 

Answer 1

The easiest way to do this problem is to look up what the angle is, divide it by 2 and look up the tan.

But you can also easily get the other trig functions since the hypotenuse of a right triangle with sides 5 and sqrt(56) is 9, then use the values of sin and cos in the half-angle formulae.