Ok I got it, your a stands for arc and arcsin means inverse sin.
Solving it is easy
tan(asin(1/3) )
let alpha = arc sin (1/3)
so 1/3=sine alpha
Draw a right angled triangle
let alpha be one of the acute angles
sine alpha = 1/3 so put the 1 on the opposite side and 3 on the hypotenuse
Use pythagoras to get the other side
Now you can read the tan value straight off the triangle
Tan(arcsin(1/3)) = 1/(square root of 8) = (root2)/4
+118654 
