The perimeter is the sum of all parties of a polygon. If several parties of a polygon have the identical size, summation at calculation of perimeter can be combined with multiplication for calculation acceleration. Ready formulas of finding of perimeter are applied to regular polygons.

## Instruction

1. To calculate perimeter at the set areas and width of a polygon, it is necessary to know to know polygon type. The "length" and "width" parameters are usually applied to characteristic of a rectangle. A rectangle is called the quadrangle with right angles and in pairs equal parties.

2. Determine rectangle length. For this purpose divide the square at width set in a condition.

3. Calculate perimeter of a rectangle on a formula P=2L+2S where P — required perimeter; S — width set in a condition; L — length calculated in item 2.

4. A special case of a rectangle — a square. All four parties of a square are equal. Therefore for calculation of perimeter it is enough to know the size of one party. Calculate square perimeter on a formula P=4S where P — required perimeter; S — width set in a condition.

5. A parallelogram - too a regular polygon. The parties in it are in pairs equal and parallel. It is impossible to calculate the size of the party of a parallelogram on the known area and other party. It is necessary to know a corner between the parties of a parallelogram. The set conditions are not enough for calculation of perimeter of a parallelogram.

6. Draw any parallelogram. On the party with a size, known for a condition, lower height from parallelogram top. With the set width and the area parallelogram height — size invariable is also equal private from division of the square at width. The corner between the parties of a parallelogram on a condition is not set. At change of a corner the size of the unknown party of a parallelogram will change. Thus the task has a set of decisions.