181k views
4 votes
A certain coin is a circle with diameter 18 mm. What is the exact area of either face of the coin in terms of pie?

User Smarie
by
8.4k points

2 Answers

4 votes

To find the area of the coin/a circle use this equation:

(a = area, r = radius, d = diameter)


\text{a = r}^2

So we need to do for the radius.


\text{r} = \frac{\text{d}}{2}


\text{r} = (18)/(2)


\text{r} = 9

Then solve


\text{a = 9}^2


\boxed{\bold{a = 81}}

User Wilcroft
by
8.7k points
5 votes

Answer:


81\pi
mm^2

Explanation:

Let's recall the formula for the area of a circle:


A = \pi r^2

We are given the diameter, but the formula uses the radius. Since the radius is equal to one-half of the diameter, we can find the radius by doing this:


r = (1)/(2)d=\\\\r=(1)/(2)(18)= \\\\r=9

Now that we've found the radius is 9 mm, let's substitute the values into the formula for the area of a circle. We have:


A = \pi r^2=\\A=\pi (9^2)=\\A=\pi (81)=\\A=81\pi

So, we've found that the exact area, in terms of pi, of either face of the coin is
81\pi
mm^2.

User Qqtf
by
8.2k points

No related questions found