Spotting angles

In your book, Maths Mela (Chapter 3), we look for angles around us and name them. A good way to check an angle is to hold the corner of a page or a notebook cover against it. That corner is a right angle, a quarter turn.

If the angle is narrower than the corner of the page, it is ACUTE. If it is wider than the corner of the page but the two arms do not yet make one straight line, it is OBTUSE. If the two arms lie in one straight line, it is a straight angle.

The book shows a house that children have built from the hard covers of notebooks. Where a wall stands straight up on the flat floor, the angle between the wall and the floor is a right angle, just like the corner of the cover. Where two covers lean against each other to make a pointed roof, the angle at the top is narrower than a right angle, so it is acute.

The book also shows five gymnasts. The first stands with her legs only a little apart, making a narrow acute angle between them. Each gymnast after her opens her legs wider: the angle grows past a right angle and becomes obtuse. The last gymnast does a full split, with her legs in one straight line: a straight angle.