### Teaching and Group Activities for Understanding

**Day 1 Teaching**

Children sketch a right-angle triangle where the sides along the right angle are 4cm and 7cm long. They measure the longest side, compare, and find the area. Draw a similar triangle with each side next to the right angle twice the length. Compare the longest sides. Define similar triangles and model the scaling effect. Remind children how to find the area of a parallelogram (see below plan), multiplying the base by the height.**Group Activities**

-- Scale up rectangles, triangles and parallelograms by a factor of 2 and 3 and see what happens to the area.

**Day 2 Teaching**

Define similar shapes as identical in shape, but not in size. Show ‘Similar shapes’ (see resources). Ask children to find 2 rectangles which look similar. Measure the sides of each. Ask children to work out the scale factor (1½). Repeat for triangles (scale factor is 3).**Group Activities**

Use the ‘Geometry genius’ in-depth problem-solving investigation below as today’s group activity.

Or, use these activities:

-- Identify pairs of similar rectangles and triangles. Use the scale factor to work out side lengths.

-- Draw similar shapes, using a scale factor of 2 or 3 or 1.5. Identify pairs of similar shapes drawn by others and find the scale factor?