There are 3 angles to the triangle but how do you know which side uses Soh, Cah, and Toa to be found?
Exclude the Right angle and the Hypotenuse to determine adjacent and opposite sides to any angle.
Out of the three angles , one is a right angle and there is a lonely hypotenuse which is opposite to right angle. Hence only two angles and two sides are left to determine which one is opposite and which one is adjacent to any of the two angles . Not a difficult task if a diagram is in front.