What is the approximate area of a circle with the radius of 1.5 ?

2 Answers
Apr 24, 2017

9pi

Explanation:

Area of a circle is pi r^2.

We're given the radius. Plug it into the formula:

pi (1.5)^2=2.25pi

That's the area of 1 circle we have four circles. So multiply this by 4"

2.25pi (4)=9pi

Apr 25, 2017

Further comment

Explanation:

There are a set of 'special' numbers that crop up all over the place and are very useful. One of them is pi

pi is the number you get if you divide the circumference of a circle by its diameter. So in effect it is a ratio. It also occurs a lot in nature.

This is what is called an irrational number. This is just a name! An irrational number is one that that has decimal values that go on for ever without any repeats. I just did a quick search and found a listing of 100,000 digits. Part of which is:

3.1415926535897932384626433832795028841971693993
75105820974944592307816406286 ....

The dots at the end mean that the digits go on a lot further.

Go back enough in time and it used to be taught that an approximation of this value is 22/7 this works out to be 3.142857...

Comparing 22/7 to 3.141562... you will observe that it starts to be different at the 3rd decimal place.

As against 22/7 a more precise approximation of pi is 3.142 which is rounded to 3 decimal places
It all depends on how precise an approximation you require. It could be argued that just the value of 3 is also an approximation.

Hope this helps

By the way: when you round a decimal it is good practice to state the number of decimal places it is rounded to. That way it indicates the potential error that creeps into the calculation.