This is how I remember the terms sin, cos, and tan. In a right triangle, the sine (sin) of an angle is the length of the side opposite the angle divided by the length of the hypotenuse (the longest side). The cosine (cos) is the length of the side next to the angle divided by the hypotenuse. The tangent (tan) is the length of the side opposite the angle divided by the length of the side next to the angle. We can be sure that sin 30 always has the same value because all right triangles with a 30 angle are similar. This means their shapes are the same, just scaled up or down, so the ratios of their sides stay the same