Logo 2: turtling triangles

Find the angle which the turtle turns in drawing an equilateral triangle.

Resources

IWB, Protractors. Plastic or card shapes: triangles. Individuals record work on plain paper.

Revision / oral

Revise the interior angles of a triangle. Recap drawing a square with Logo.

If two angles of a triangle are both 70 degrees, what is the third angle?

If the first angle is 85 degrees and the second is 25 degrees, what is the third angle?

Key vocabulary

 Interior angle, exterior angle, equilateral triangle, facing, heading

Main activity

How are we going to tell the turtle draw an equilateral triangle? The turtle is facing up the screen. Draw the possibilities with a pen on the board:

Focus on the turtle facing a particular direction. The screen display enables the whole class to see this. Children need to identify the angle that the turtle has to turn through. They need to see the shape from the turtle's viewpoint.

The class work on plain paper, drawing the triangle with the help of a protractor, then writing the commands below. Draw the class together to try out some of their 'programs'. It's very likely that 60 degree turns will feature:

It's important to establish an atmosphere where children are not afraid to make mistakes, but where they see that feedback from the computer is helpful in planning the next step.

Support

Some children find it difficult to relate to the turtle's angle of turn. Ask them to pace round a triangle. Extend an arm in front, to show turning. Is it more or less than 90 degrees? Now look at the amount of turn in relation to the turtle's original heading:

If plastic or card shapes are available, children may trace their fingers round the edges to 'feel' the corners.

Challenge

Other types of triangle can be drawn (isosceles, scalene). Finding the length of the third side challenges pupils' ability to estimate in Logo units. Constructing the shape on paper and determining a scale (e.g. 1 cm = 25 units) will help.

Plenary

Discuss why the turtle needs to turn 120 degrees, not 60. If the turtle continued to turn 60 degrees, what shape would it draw? Can the class predict how to draw other polygons?

In every case - square, triangle, hexagon - what is the sum of turtle turns (given that it returns to face its original heading)?