Draw the picture in the first quadrant.
Since tan(x) = opposite / adjacent = 1 / 3,
the opposite side = 1 and the adjacent side = 3
Using the Pythagorean Theorem: hypotenuse2 = opposite2 + adjacent2
= 12 + 32 = 10
hypotenuse = sqrt(10)
sin(x) = opposite / hypotenuse = 1 / sqrt(10)
cos(x) = adjacent / hypotenuse = 3 / sqrt(10)
You should place each of these answers in simplest radical form.