How do you know when to use sin, cos and tan?

When trying to work out and unknown angle in a right angled triangle, if you know the length of two sides you can use these the figure out the right trig function to use. SOH CAH TOA is an easy way to remember which function to use:-If you have the length of the side opposite of the unknown angle and the hypotenuse you use sin - SinOppositeHypotenuse-If you have the length of the adjacent side to the unknown and the hypotenuse you use cos - CosAdjacentHypotenuse-If you have the length of the opposite and the adjacent side to the unknown you use tan- TanOppositeAdjacent