Skill: Use complementary angles informally

Complementary angles are two angles that add up to $90^\circ$. A right angle measures $90^\circ$, so complementary angles fit together to make a right angle.

Example

One angle measures $35^\circ$. Find its complement.

1. Start with the whole right angle:

$$90^\circ$$

2. Subtract the known angle:

$$90^\circ-35^\circ=55^\circ$$

3. The missing angle is therefore:

$$\boxed{55^\circ}$$

Check your answer:

$$35^\circ+55^\circ=90^\circ$$

So, $35^\circ$ and $55^\circ$ are complementary angles. They do not have to be equal, but their measures must add to $90^\circ$.