When we talk about right-angled triangles, there are three important ratios you should know:

1. Sine (sin): This ratio looks at the opposite side compared to the hypotenuse. You can remember it like this:
   $\text{sin}(A) = \frac{\text{opposite}}{\text{hypotenuse}}$

2. Cosine (cos): This one checks the adjacent side against the hypotenuse. It's written as:
   $\text{cos}(A) = \frac{\text{adjacent}}{\text{hypotenuse}}$

3. Tangent (tan): This ratio compares the opposite and adjacent sides. You use it like this:
   $\text{tan}(A) = \frac{\text{opposite}}{\text{adjacent}}$

These ratios are really useful for solving problems about angles and sides in triangles!