**Introduction to learning shape of circle:**

Learning circle shape will help to draw and identify the circle.. Learning shapes is a basic steps to learn calculate the area and circumference of the circle.These learning skills used to recognize the circle from other shapes. Some of these ideas are properly educate the students with individuality and support their ideas.

**Definition of circle:**

Central point to all locus of points.

**Related titles to circle:**

**Arc:** Curve line.

**Chord:** Line segment that is connect two points.

**Circumference:** Around the circle, how much distance are present.

**Diameter:** Distance between two ends of the circle.

**Origin:** Center of shape.

**Radius:** Distance between any point on circle to center of circle.

**Unit circle:**

It is defined as a circle which has radius of 1.

Equation of unit circle: x^{2}+y^{2}=1.

We can measure sin, cos and tan values directly.30°,45°,60° angle values are defined in particular table.Using this table, we can calculate every measurement of the circle.

Learning formulas for circle shape:

**Diameter**=2 x radius

**Circumference** = PI x diameter

(or)

**Circumference** = 2 PI x radius

**Circle area** = PI x r x r

**Arc length** = Θ x (PI/180) x r (angle in degree)

(or)

**Arc length** = r x Θ (angle in radian)

**Circle sector are**a = ( Θ/360) PI r^{2} (angle in degree)

(or)

**Circle sector area** = ( Θ/2) r^{2} (angle in radian)

Equations of circle is fully based on coordinates like cartesian, polar, parametric.Each coordinates has center and radius value.

**Cartesian coordinates:**

**Circle equation** : (x-j)^{2} + (y-k)^{2} = r ^{2}

Center (j,k) and radius (r)

**Polar coordinates:**

If center (0,0): r(Θ)=radius.

If polar coordinates (c,α) and radius a:

r^{2}-2cr cos(Θ-α) + c^{2} = a^{2}

**Parametric coordinates:**

Origin (j,k) and radius r:

X(t) = r cos(t) + j , y(t) = r sin(t) + k