**Perimeter of a Triangle:**

If a, b and c units be the lengths of the sides of a triangle, perimeter = a + b + c

or 2s = a + b + c, where 2s denotes the perimeter of the triangle.

**Heron’s Formula for Area of a Triangle:**

If a, b and c are the sides of a triangle and 2s = a + b + c, the area of the triangle is given by:

A = √s(s - a)(s - b)(s - c)

**Area of an Equilateral Triangle:**

**Theorem 1:**

► Parallelogram on the same base and between the same parallels is equal in area.

**Theorem 2:**

**► ****Circle** is the locus of all such points which are equidistant from a fixed point, this point is known as **centre** while distance of any point from centre defined as **radius** of circle.

► A line joining two points on a circle is known as the **chord** of the circle.

A line which intersects a circle in two distinct points is called a **secant** of the circle.

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