Memorize the mnemonic "SOHCAHTOA," which is pronounced "soak a toe uh."
Break SOHCAHTOA down into three parts: SOH, CAH and TOA. Each mnemonic describes a way to solve for an unknown angle in a right triangle depending on the what information is given.
Translate SOH as Sine Opposite over Hypotenuse. This means you can solve for an unknown angle by setting up a fraction with the length of the opposite side of the triangle as the numerator and the hypotenuse as the denominator, multiplied by sine.
Translate CAH as Cosine Adjacent over Hypotenuse. This means you can solve for an unknown angle by setting up a fraction with the length of the adjacent side as the numerator and the hypotenuse as the denominator, multiplied by cosine.
Translate TOA as Tangent Opposite over Adjacent. This means you can solve for an unknown angle by setting up a fraction with the length of the opposite side as the numerator and the adjacent side as the denominator, multiplied by tangent.
Start each problem by drawing a small diagram of all known information.
Solve for the unknown angle by determining which trigonometric ratio you need to use, depending on which angle is unknown and what other information is available. For example, if you know the length of the side opposite the unknown angle and the length of the hypotenuse, you can use the "SOH" method to construct a formula to find the unknown angle.