Skill: Use the triangle angle sum

The three interior angles of every triangle add up to $180^\circ$.

To find a missing angle:

1. Add the two known angles.
2. Subtract that sum from $180^\circ$.
3. Include the degree symbol.

Example: A triangle has angles measuring $65^\circ$, $45^\circ$, and $x^\circ$. Find $x$.

First, write an equation using the triangle angle sum:

$$65^\circ+45^\circ+x^\circ=180^\circ$$

Add the known angles:

$$110^\circ+x^\circ=180^\circ$$

Subtract $110^\circ$ from both sides:

$$x^\circ=180^\circ-110^\circ=70^\circ$$

So, the missing angle is:

$$\boxed{70^\circ}$$

Check: $65^\circ+45^\circ+70^\circ=180^\circ$, so the answer is correct.