Why Do Angles In A Triangle Add Up To 180 Degrees?

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Why do Angles in a Triangle Add to 180 Degrees?

To investigate the sum of the angles in a triangle, we can begin by marking each angle with a different colour.

A triangle with its 3 angles marked

We can use this to find out what the angles in a triangle add up to.

If we move these angles so that they fit in next to each other, we can see that they rest on a straight line.

3 triangle angles placed on a straight line to equal 180 degrees

Angles on a straight line add up to 180°.

Therefore, angles in a triangle also add up to 180°.

You can test this at home by following these steps:

1) Cut out a triangle

A grey triangle

2) Mark the outer angles

A triangle with its angles marked

3) Cut these angles off

A triangle with its angles marked

4) Place these marked angles together

3 angles of a triangle placed together

You should be able to place these angles onto a straight line.

3 angles of a triangle placed together to make a straight line

Angles in a triangle add up to 180°. Now try

Finding a Missing Angle in a Triangle: Subtraction from 180 Degrees