Use four small squares with a side length of 1 cm to spell out three different shapes. Tell me what the perimeter of these figures is.

① Make a rectangle with four small squares, with side length 1 cm and perimeter 10 cm.

(4+ 1)×2

=5×2

= 10 (cm)

② Make a T-shape with four small squares with side length of 1cm and perimeter of 1cm.

(3+2)×2

=5×2

= 10 (cm)

③ Make a square with four small squares, with a side length of 1 cm and a circumference of 8 cm.

2×4

=8 cm

④ Four small squares with a side length of 1cm form an L-shape with a perimeter of 1cm.

(3+2)×2

=5×2

= 10 (cm)

Area and perimeter

If it is a triangle with the same area, the perimeter of an equilateral triangle is the shortest; If it is a quadrilateral with the same area, the perimeter of the square is the shortest; If pentagons with the same area are used, the perimeter of regular pentagons is the shortest; If you use any polygon with the same area, the circumference of a regular circle is the shortest.

Perimeter can only be used on two-dimensional figures (planes and surfaces), and three-dimensional figures (solids) such as cylinders, cones and spheres can't express their boundary size by perimeter, but by total surface area.

Total surface area = the total area of all sides of a solid.