Remember SOH CAH TOA, sound it out and remember that 'phrase.
The first letter represents the function (sin, cos, tan). The second letter represents the numerator and the third letter represents the denominator.
By this logic, we'd go to SOH, and the top would be O (opposite) and the bottom would be H (hypotenuse).
\(\sin (\theta ) = \frac{opposite}{hypotenuse}\)
