Draw a right triangle, with an angle A:



Since the numerator of  is 1 and the denominator of
 is 2, and since the tangent is 

let's label the side opposite A as 1 and the side adjacent to A as 2:



Now we can calculate the hypotenuse by the Pythagorean theorem:







Now we have this:



Now since the sine is 



and if your teacher makes you rational the denominators
of such expressions, the answer is 



Edwin