The set square and figures of rectangles

In Russian schools (Grade 4, "Spatial relations and geometric figures" and "Geometric quantities") children draw a right angle and perpendicular lines with a set square and find the area and perimeter of figures made of rectangles.

To find the area of such a figure, split it into rectangles, find the area of each (length × width, in cm²) and add. The usual slips are to take the area of the box around the figure or to count a part twice.

Here the square-corner card plays the set square. In a real exercise book, hold a real set square against the drawing.