**Finding the area of a circle :**

In this section, we are going to see the formula for area of a circle and also how the formula can be used to find area of a circle.

The formula given below is used to find area of a circle.

**Question 1 : **

Find the area of a circle whose radius is 7 cm.

**Answer :**

**Step 1 : **

Area of a circle = πr²

Radius is given in the question. That is 7 cm.

Plug r = 7 in the above formula.

Area of the circle = π(7)²

**Step 2 : **

Since radius is a multiple of 7, we can use π ≈ 22/7.

Area of the circle ≈ (22/7) x (7)²

Simplify

Area of the circle ≈ 22 x 7

Area of the circle ≈ 154 square cm.

Hence, the area of the circle is about 154 square cm.

**Question 2 :**

Find the area of a circle whose diameter is 40 inches.

**Answer :**

**Step 1 : **

Area of a circle = πr²

We know that

Radius = Diameter / 2

Radius = 40/2 = 20 inches

**Step 2 : **

Plug r = 20 in the above formula.

Area of the circle = π(20)²

**Step 3 :**

Since radius is not a multiple of 7, we can use π ≈ 3.14.

Area of the circle ≈ (3.14) x (20)²

Area of the circle ≈ 3.14 x 400

Area of the circle ≈ 1256 square in.

Hence, the area of the circle is about 1256 square in.

**Question 3 :**

A biscuit recipe calls for the dough to be rolled out and circles to be cut from the dough. The biscuit cutter has a radius of 4 cm. Find the area of the top of the biscuit once it is cut. Use 3.14 for π.

**Answer :**

**Since the top of the biscuit is in the shape of a circle, we can use area of circle formula to find area of the top of the biscuit. **

**Step 1 : **

Area of a circle = πr²

Radius is given in the question. That is 4 cm.

Plug r = 4 in the above formula.

Area of the circle = π(4)²

**Step 3 :**

Since radius is not a multiple of 7, we can use π ≈ 3.14.

Area of the circle ≈ (3.14) x (4)²

Area of the circle ≈ 3.14 x 16

Area of the circle ≈ 50.24 square cm.

The area of the biscuit is about 50.24 square cm.

**Question 4 :**

Compare finding the area of a circle when given the radius with finding the area when given the diameter.

**Answer :**

The formula for area of a circle uses the radius of the circle. If we are given the diameter of the circle, we must first divide it by two to get the radius.

**Question 5 :**

Why do we evaluate the power in the equation before multiplying by pi ?

**Answer :**

We must follow the order of operations and evaluate the exponents before multiplying.

**Question 6 :**

When is it logical to use 22/7 instead of 3.14 for π ?

**Answer :**

When the radius or diameter is a multiple of 7

After having gone through the stuff given above, we hope that the students would have understood "Finding the area of a circle".

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