Trigonometry is a branch of mathematics that deals with the relationships between the sides and angles of triangles. In trigonometry, we use three main trigonometric ratios: sine (sin), cosine (cos), and tangent (tan).

To find the sine, cosine, or tangent of an angle in a right-angled triangle, we can use the following formulas:
- Sine (sin) = Opposite side / Hypotenuse
- Cosine (cos) = Adjacent side / Hypotenuse
- Tangent (tan) = Opposite side / Adjacent side

For example, let's consider a right-angled triangle with one angle measuring 30 degrees. If the opposite side is 5 units and the hypotenuse is 10 units, we can find the sine of 30 degrees as:
sin(30 degrees) = Opposite side / Hypotenuse
sin(30 degrees) = 5 / 10
sin(30 degrees) = 0.5

Similarly, we can find the cosine and tangent of 30 degrees using the given sides of the triangle.

By understanding and applying these trigonometric ratios, we can solve various problems involving triangles and angles.