Angles in flat shapes

In your book, Maths Mela (Chapter 1), you sort flat shapes by their angles. Every corner of a flat shape is an angle, and every corner is where two sides meet. So a shape has as many angles as it has sides. A triangle has 3 sides and 3 angles. A four-sided shape has 4 angles. A pentagon has 5 sides and 5 angles.

Next, count the right angles. A rectangle has 4 angles and all 4 are right angles. A square has 4 right angles too. A triangle can have 1 right angle, like the corner of a book; we call it a right-angled triangle. Its other 2 angles are acute.

Your book also shows a parallelogram, a rhombus and a trapezium. They are four-sided shapes too, but the ones in the book are slanting: they have acute and obtuse angles. That is how a rectangle and a square are different: they have only right angles.

A square is a special rectangle: it has 4 right angles like every rectangle, and all four of its sides are equal as well. A triangle or a pentagon can never have only right angles: a triangle has at most 1 right angle, and a pentagon's corners cannot all be right angles either.