But anyway, that’s enough accuracy to give our answer correct to decimal places. Now when I type ten times 𝜋 on my calculator, I get thirty-one point four one five nine two six five four, and then my calculator runs out of digits. We’re gonna have to use our calculator and get an approximation. 𝜋 is an irrational number, which means it’s got an infinite number of decimal places and they’re constantly changing, so we can’t hope to remember all of that number. So our answer in terms of 𝜋 is ten 𝜋 units, but the question didn’t ask for that it asked us to give our answer accurate to two decimal places. So all I need to do is to plug the radius into that formula, so the circumference is two times 𝜋 times the radius of five, and two times five is ten. And since we’ve been given the radius in our question, then I think we’ll use this version of the formula. Now we’ve got two different formulae for working out the circumference: two times 𝜋 times 𝑟, where 𝑟 is the radius, or 𝜋 times 𝑑, where 𝑑 is the diameter. Now the question asks us to work out the length of the circumference of the circle. So the radius of our circle is five units. Now, 𝑂𝐴 marks out the distance here from the centre of the circle to its circumference, and we’ve got a special name for that it’s the radius of the circle.
So we’ll just have to write that on our diagram. So we’re told that length 𝑂𝐴 equals five, and we’re not actually told what the units are, so we don’t know whether they’re metres, miles, inches, whatever.
Work out the circumference of the circle given that 𝑂𝐴 equals five, giving your answer accurate to two decimal places.
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