Angles on a Straight Line and at a Point

In a Nutshell

Angles on a straight line add up to $180°$ . Angles at a point add up to $360°$ .

Angles on a straight line

When two or more angles sit on one side of a straight line, they form a half turn. A half turn is $180°$ , so the angles must add up to $180°$ .

When angles meet at a single point and together make a full turn, they add up to $360°$ .

These two facts let you find a missing angle whenever you know the others. Set up an equation and solve.

Choose "Straight line" or "At a point" and adjust the angle to see how the remaining angle changes to keep the total correct.

Question: Two angles on a straight line are $x$ and $125°$ . Find $x$ .

Q1. Two angles on a straight line are $73°$ and $x$ . Find $x$ .

Q2. Three angles on a straight line are $40°$ , $65°$ and $y$ . Find $y$ .

Q3. Three angles meet at a point: $120°$ , $150°$ and $z$ . Find $z$ .

Q4. Four angles meet at a point. Three of them are $80°$ , $100°$ and $90°$ . Find the fourth angle.