Angles

Hello, and welcome to Myriora Maths! When you turn, you turn through an angle. Angles are measured in degrees. Let's meet the different kinds of angle, and learn to measure them.

A full turn, all the way round, is three hundred and sixty degrees. A half turn is a hundred and eighty degrees. And a quarter turn is ninety degrees: a right angle, like the corner of a book.

An angle smaller than a right angle is acute. An angle bigger than a right angle, but smaller than a straight line, is obtuse. A straight line is a hundred and eighty degrees. And an angle bigger than that is a reflex angle.

To measure an angle, use a protractor. Put its centre on the corner of the angle. Line up the zero with one of the arms. Then read the scale where the other arm crosses, counting up from that zero.

Let's try one together. An angle is forty degrees. Is it acute, obtuse or reflex? Say it out loud!

Forty degrees is smaller than a right angle. So it's acute!

Here's a question that catches lots of people. This angle is clearly smaller than a right angle. But some people read the wrong scale on the protractor, and say a hundred and twenty degrees. Start from the zero on the arm you lined up, and count up: it's sixty degrees. Always check: is the angle acute or obtuse?

Your turn! What kind of angle is a hundred and thirty-five degrees? Pick the right card. You've got twenty seconds, or pause the video. Go!

Time's up! A hundred and thirty-five is bigger than ninety, but smaller than a hundred and eighty. So it's obtuse!

Quick review. A right angle is ninety degrees, a straight line is a hundred and eighty, and a full turn is three hundred and sixty. Acute is smaller than ninety, obtuse is between ninety and a hundred and eighty, and reflex is bigger than a hundred and eighty. To measure, start from zero and count up. See you next time!