Use formulas correctly for calculating circles

Formulas for calculating circles - you need these

• When calculating circles, there are actually - apart from special tasks - only two important formulas, namely the one for the circumference and the one for the area of ​​the circle.
• For both formulas you need the circle number ¶ (read: Pi), which you can approximate to 3.14 when doing handwritten calculations. You will receive more precise values ​​from calculator.
• The formula for the circumference is U = 2 ¶ r, where U stands for the circumference and r for the radius of the circle.
• The formula for the circular area is A = ¶ r². A is the abbreviation for area.
• The radius r of a circle can easily be calculated from the diameter d. The following applies: r = 1/2 d.


Calculate a semicircle - this is how it works

Can a semicircle be a challenge? With these simple formulas you can ...

Circle calculation on a pizza - this is how it's done

In the case of a round pizza, it is less the circumference that is of interest, but rather the area (and whether it is large enough). So of the two formulas you need the one for the area of ​​the circle.

For the example, areas and prices are to be compared for these two pizza offers, provided that the topping is the same:

• Pizza No. 1 (large) has a diameter of 35 cm and costs 7.50 euros.
• Piiza No. 2 (small) has a diameter of 28 cm and costs 6 euros.

You want to decide which of the two offers is cheaper and use the circular formulas as follows:

1. The area for pizza no. 1 is A = ¶ r² = ¶ (35/2) ² = 962 cm²
2. The area for pizza no. 2 is A = ¶ (28/2) "= 616 cm² (rounded up).
3. The area ratio is therefore 962 cm²: 616 cm² = 1.56
4. Calculate the price ratio at 7.50 euros: 6 euros = 1.25.

Well how would you choose? Big Pizza # 1 is actually bigger in relation to the price. So if you are hungry, things should be clear!