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

Best way to remember it is: soh, cah and toa.Where soh means that the sine of the angle is equal to the length of the opposite side divided by the length of the hypotenuse.Cah means that the cosine of the angle is equal to the length of the adjacent side divided by the length of the hypotenuse.Toa means that the tangent of the angle is equal to the length of the opposite side divided by the length of the adjacent side.sin(angle)= o/h cos(angle)=a/h tan(angle)=o/a hence soh cah toa. However, this can only be used in right angle triangles.