Angles in Triangles and Quadrilaterals

Can you have a triangle with two obtuse angles?

Is it possible to have a quadrilateral with exactly three right angles?

How small can the largest angle in a triangle be?

Well first you can have a go at investigating these questions by drawing or making shapes.

But if you then draw a whole load of triangles and quadrilaterals, measure the angles and add them together, you begin to discover something interesting! All the angles in a triangle add to the same total. And so do all the angles in a quadrilateral.

Does it work for any triangle and any quadrilateral?

The secret learning intention behind this investigation is how to use a protractor properly! And along the way you will have some useful discussions about the different kinds of triangle and quadrilateral. (To go into this in more depth, see the investigation on properties of quadrilaterals.)

Ages 8-12    Printable materials (pdf) - 3 pages of teacher's notes and 4 pupil copymasters.