To solve problems about triangles in geometry, there are some helpful strategies you can use:

1. Know the Types of Triangles:

   • Scalene: All sides and angles are different.
   • Isosceles: Two sides are the same, and the angles opposite those sides are also the same.
   • Equilateral: All sides and angles are the same, and each angle is $60^\circ$.
   • Right Triangle: One angle is $90^\circ$. This lets us use a special rule called the Pythagorean theorem.

2. Use the Pythagorean Theorem: For right triangles, we have a rule about the sides: $a^2 + b^2 = c^2$ Here, $c$ is the longest side called the hypotenuse. This rule helps us find missing side lengths. It's useful in real life, like in construction or navigation.

3. Understand Angle Properties:

   • The angles inside any triangle add up to $180^\circ$.
   • In isosceles triangles, the angles at the base are the same.
   • The exterior angle rule states that the outside angle equals the sum of the two inside angles that aren't next to it.

4. Remember the Triangle Inequality Theorem: This rule tells us that for any triangle with sides $a$, $b$, and $c$:

   • $a + b > c$
   • $a + c > b$
   • $b + c > a$

5. Practice with Real-Life Problems: Try using triangle properties in real life. You can work on things like making scale models or measuring heights from a distance.

By learning these strategies and the different properties of triangles, students in Year 9 can solve many kinds of geometry problems more easily.