**Angles on one side of a straight line**

The angles on one side of a straight line always add to 180 degrees.

When a line is cut into two and we know one angle, we can always find the other one.

The two angles are supplementary, which means they add to 180 degrees.

For example, if one angle is 40 degrees we know the other angle is 140 degree.

**Angle a equals 1**8**0**°**- 40**°** = 140**°

or if one angle is 80 degrees we know the other angle will be 100 degrees.

**Angle a equals 180****°**** ****- 80****°**** = 100****°**

This method can be used for several angles on one side of a straight line.

**Example: What is angle "b" in the picture above?**

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