All the Angles Add up

We have been looking at angle this week and last week and even having taught everything about angles years ago. I still managed to learn something. Or at least understand why a fact I was told is valid. 

Facts I was told

• Angles inside a triangle add up to 180 degress
• Angles on a straight line add up to 180 degrees
• Angles around a point add up to 360 degrees

The last too facts were easy to get thanks to a protractor, all the way from the beginning of a circle to the end is 360 degrees, easy. Draw a straight line and measure using a protractor from one side to the other 180 degrees. No sweat.

The first one I just learnt as a fact. That was fine, maths is made up of plenty of facts I just learnt, like times tables. 

I never (or at least I don't remember) thought about a triangle as part of two parallel lines, and of course the lines on a straight line equal 180 degrees.