Area and Perimeter of Plane Figure

**Perimeter**is the length of the boundary of a closed figure.- The perimeter of a polygon is the sum of the lengths of all its sides.

In case of a triangle ABC, with sides of lengths *a*, *b* and *c* units:

Perimeter of ABC = AB + BC + AC = *a* + *b* + *c*

- The
**semi-perimeter**of a triangle is half the perimeter of the triangle.

The semi-perimeter (*s*) of a triangle with sides *a*, *b* and *c* is.

- The semi-perimeter of a triangle is used for calculating its area when the length of altitude is not known.

- Area of a triangle:
- Area of a triangle =
- All the congruent triangles are equal in area, but the triangles having equal areas may or may not be congruent.

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