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4.7 A) Circle Introduction
4.7 A) Circle Introduction
Below is a diagram of a circle.
The centre of the circle is literally the centre point of the circle. On the above circle I have drawn on the radius and the diameter of the circle.
The radius is the distance between the outside of the circle and the centre of the circle. There are an infinite number of radiuses on any circle and the radius will always be the same length.
The diameter of a circle is the distance from one side of the circle to the other side of the circle through the centre of the circle. The diameter is twice the length of the radius (or you can say that the radius is half the length of the diameter). There are an infinite number of diameters on any circle and the diameters will always be the same length.
The radius is the distance between the outside of the circle and the centre of the circle. There are an infinite number of radiuses on any circle and the radius will always be the same length.
The diameter of a circle is the distance from one side of the circle to the other side of the circle through the centre of the circle. The diameter is twice the length of the radius (or you can say that the radius is half the length of the diameter). There are an infinite number of diameters on any circle and the diameters will always be the same length.
Working Out the Radius/ Diameter
Often in the exam, you will be given the radius of a circle and asked to work out some information that will require you to work out the diameter (or vice versa).
In the above paragraph we learnt that the diameter is twice the length of the radius, which is the same as saying that the radius is half the length of the diameter.
This means that if we are given the radius of a circle and want to find out what the diameter of the circle is, we will double what the radius of the circle is.
If we are given the diameter of a circle and want to find out the radius of the circle, we will divide it by two.
The formula is shown below:
Often in the exam, you will be given the radius of a circle and asked to work out some information that will require you to work out the diameter (or vice versa).
In the above paragraph we learnt that the diameter is twice the length of the radius, which is the same as saying that the radius is half the length of the diameter.
This means that if we are given the radius of a circle and want to find out what the diameter of the circle is, we will double what the radius of the circle is.
If we are given the diameter of a circle and want to find out the radius of the circle, we will divide it by two.
The formula is shown below:
Let’s have a few examples.
Example 1
We are given the following circle that has a radius of 4 cm. What is the diameter of the circle?
We are given the following circle that has a radius of 4 cm. What is the diameter of the circle?
We are given the radius of the circle and are asked to work out the diameter of the circle. In order to do this, we need to multiply the radius of the circle by 2.
The diameter of the circle is 8 cm.
Example 2
A cake has a diameter of 14 cm. What is the radius of the circle?
A cake has a diameter of 14 cm. What is the radius of the circle?
We are given the diameter and we know that the radius is going to be half the length of the diameter. Therefore, we divide the diameter by 2.
The radius of our cake is 7 cm.