How to find the area of a circle in pre-algebra - Math

Card 0 of 108

Question

What is the area of a circle with diameter ?

Answer

The area of a circle is calculated with the equation $A=\pi r^2$ .

is half of the diameter, which in our case is 3.

$A=\pi r^2= (3)^2\pi=9\pi$

Compare your answer with the correct one above

Question

Find the area of a circle with a radius of 12 inches.

Answer

The formula for the area of a circle is $A=\pi r^2$ .

Plug your radius value in and you get $144\pi$ .

Make sure your units are squared.

Compare your answer with the correct one above

Question

Find the area of a circle with a radius of 7 inches.

Answer

Use the formula for the area of a circle, $A=\pi r^{2}$ , and plug in 7 for the radius to get $49\pi$ . Make sure your answer is in units squared.

Compare your answer with the correct one above

Question

What is the area of circle with a radius of ?

Answer

To find the area of a circle you must plug the radius into in the following equation

In this case the radius is so we plug it into to get $9^{2}=81$

We then multiply it by $\pi$ to get our answer $A=81\pi$ .

Compare your answer with the correct one above

Question

What is the area of a circle with radius of ?

Answer

The formula for the area of a circle is $A=\pi r^2$ .

Plug in our given values:

$A=\pi r^2$

$A=\pi*3^2$

$A=9\pi$

Compare your answer with the correct one above

Question

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

Answer

The formula for the area of a circle is $A=\pi r^2$ .

Plug in the information given and solve:

$A=\pi * 4^2$

Remember, a number squared is just the same as that number times itself:

$A=\pi(44)$

$A=16\pi$

Compare your answer with the correct one above

Question

If the area of a circle is $64\pi$ , what is the radius of the circle?

Answer

The formula for the area of a circle is $A=\pi r^2$ .

Plug in the information given and solve:

$64\pi = \pi r^2$

Notice that the $\pi$ 's cancel out:

Take the square root of both sides:

$\sqrt{64}=\sqrt{r^2}$

Compare your answer with the correct one above

Question

If the diameter of a circle is , what is the area of that circle?

Answer

The area of a circle is $A=\pi r^2$ , but the problem gives us the diameter and not the radius.

The diameter is twice the radius, so . We can plug in our given values to find the radius:

$\frac{22}{2}=r$

Now we can plug this value into our equation for area:

$A=\pi r^2$

$A=\pi11^2$

$A=\pi 121$

$A=121\pi$

Compare your answer with the correct one above

Question

If the area of a circle is $36\pi$ , what is the length of the radius?

Answer

The formula for the area of a circle is $A=\pi r^2$ . Plug in our given information to solve:

$A=\pi r^2$

$36\pi=\pi r^2$

The $\pi$ 's cancel out, leaving us with:

Take the square root of both sides:

$\sqrt{36}=\sqrt{r^2}$

Compare your answer with the correct one above

Question

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

Answer

To find the area of a circle, you must plug the radius in for in the following equation:

In this case the radius is , so we plug in for to get $A=\pi(4^{2})$ .

$A=16\pi$

Compare your answer with the correct one above

Question

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

Answer

The formula for area of a circle is $A=\pi r^2$ .

Plug in our given information:

$A=\pi*5^2$

$A=25\pi$

Compare your answer with the correct one above

Question

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

Answer

The formula for area of a circle is $A=\pi r^2$ .

Plug in our given information:

$A=\pi 6^2$

$A=36\pi$

Compare your answer with the correct one above

Question

What is the area of a circle with a diameter of ?

Answer

The formula for area of a circle is $A=\pi r^2$ . However, the problem gives us the diameter instead of the radius. The diameter is twice the length of the radius:

$\frac{22}{2}=r$

We can plug that back into our area equation:

$A=\pi r^2$

$A=\pi *11^2$

$A=121\pi$

Compare your answer with the correct one above

Question

What is the area of a circle with a diameter of ?

Answer

The formula for area of a circle is $A=\pi r^2$ . However, the problem gives us the diameter instead of the radius. The diameter is twice the length of the radius:

$\frac{12}2{}=r$

We can plug that back into our original equation and solve:

$A=\pi r^2$

$A=\pi *6^2$

$A=36\pi$

Compare your answer with the correct one above

Question

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

Answer

The formula for the area of a circle is $A=\pi r^2$ .

Plug in our given radius.

$A=\pi r^2$

$A=\pi *2.5^2$

$A=6.25\pi$

Compare your answer with the correct one above

Question

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

Answer

The formula for the area of a circle is $A=\pi r^2$ .

Plug in our radius.

$A=\pi r^2$

$A=\pi 8^2$

$A=\pi64$

$A=64\pi$

Compare your answer with the correct one above

Question

What is the area of a circle with a diameter of ?

Answer

The formula for area of a circle is $A=\pi r^2$ , but the problem gives us the diameter and not the radius.

The diameter is twice the radius, so . Therefore .

Plug this value into our given equation.

$A=\pi r^2$

$A=\pi (7)^2$

$A=\pi *49$

$A=49\pi$

Compare your answer with the correct one above

Question

What is the area of a circle with diameter of ?

Answer

The formula for the area of a circle is $A=\pi r^2$ .

The problem gives us the diameter, however, and not the radius. Since the diameter is twice the radius (), then if the diameter is , the radius will be .

Plug that into our given equation.

$A=\pi r^2$

$A=\pi (4)^2$

$A=\pi*16$

$A=16\pi$

Compare your answer with the correct one above

Question

What is the area of a circle with diameter of ?

Answer

The formula for the area of a circle is $A=\pi r^2$ .

The problem gives us the diameter, however, and not the radius. Since the diameter is twice the radius (), if the diameter is , the radius will be .

Plug this value into our given equation:

$A=\pi r^2$

$A=\pi (8)^2$

$A=\pi*64$

$A=64\pi$

Compare your answer with the correct one above

Question

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

Answer

To find the area of a circle you must plug the radius into in the following equation

In this case the radius is so we plug it into to get

We then multiply it by to get our answer .

Compare your answer with the correct one above

Tap the card to reveal the answer