Skill: Identify right angles

A right angle is a square corner. It is made by a quarter turn, or $90^\circ$. The corner may point up, down, or sideways, and the sides can be different lengths.

To identify one:

1. Look at the two sides or rays that meet.
2. Imagine turning from one side to the other.
3. If the turn makes a square corner, it is a right angle.
4. A small square mark at the corner is another clue that it is a right angle.

Example: Identify the right angles in this rectangle.

A ┌────────┐ B
  │        │
D └────────┘ C

• At corner $A$, the top side and left side make a square corner. So $A$ is a right angle.
• At corner $B$, the top side and right side make a square corner. So $B$ is a right angle.
• At corner $C$, the right side and bottom side make a square corner. So $C$ is a right angle.
• At corner $D$, the bottom side and left side make a square corner. So $D$ is a right angle.

Therefore, the rectangle has four right angles. Each one measures $90^\circ$.