Triangles are really important for learning about angles in geometry, especially in Year 9. Here's how they fit in:

1. Types of Triangles: There are different kinds of triangles like right, acute, and obtuse. Knowing these helps us understand different angles better. For example, a right triangle has one angle that is $90^\circ$. This is an important reference point when we compare other angles.

2. Angle Sum Property: In any triangle, all the angles add up to $180^\circ$. This rule is super important for understanding how angles work together in different shapes.

3. Pythagorean Theorem: This rule, written as $a^2 + b^2 = c^2$, is very important for right triangles. It helps us figure out the lengths of the sides and strengthens our understanding of angles, especially with right angles.

All these points show that triangles are a key part of geometry!