Enter one known value of a circle and calculate the area, circumference, radius or diameter. You will get solution with step-by-step explanation.
To calculate missing value in circle, based on one known value, you need to remember just three formulas.
F1: | $$ A = r^2 \cdot \pi $$ |
A = area C = circumference r = radius d = diameter |
F2: | $$ C = 2 \cdot r \cdot \pi $$ | |
F3: | $$ d = 2 \cdot r $$ |
The diagram at the right shows when to use each of these formulas.
Find circumference of a circle when the area is 20.
To solve this problem we first need to find radius $r$, by using formula $ \color{blue}{A = r^2 \pi} $ (see the diagram).
$$ \begin{aligned} & \color{blue}{A = r^2 \pi} \\ & 20 = r^2 \pi \\ & r^2 = \frac{20}{\pi} \\ & r^2 = \frac{20}{3.14} \\ & r^2 = 6.37 \\ & r = \sqrt{6.37} \\ & r = 2.52 \end{aligned} $$Now we will find circumference using the formula $\color{blue}{C = 2r\pi} $.
$$ \begin{aligned} & \color{blue}{C = 2 r \pi} \\ & C = 2 \cdot 2.52 \cdot 3.14 \\ & C = 15.82 \end{aligned} $$Quick Calculator Search
Please tell me how can I make this better.