Plug in the numbers and solve for C. Look back at the original word problem to see what the diameter equals, and replace the d in this equation with that number. Method 3. Understand how the area of a circle is calculated. Most of the time, people don't measure the area A of a circle directly. The reason why this formula makes sense is a little tricky, but you can find out more here if you are interested and willing to tackle some tougher algebra. Learn a formula for calculating the circumference.
The circumference C is the distance around the circle. Use the area formula to get r on one side. If the steps below are difficult for you to follow, you might want to start on some easier algebra problems or try some techniques for understanding algebra. Change the circumference formula using what you found. For this problem, we don't know the value of r, but we do know the value of A.
Plug in the numbers to find the circumference. Use the area given by the problem to solve for the circumference. Remember to include the parentheses. Method 4. Use this method to measure real circular objects. You can measure the circumference of circles you find in the real world, not just in word problems. Try it out on a bicycle wheel, a pizza, or a coin. Find a piece of string and a ruler. The string must be long enough to wrap around the circle once, and flexible enough that it can wrap tightly.
You'll need something to measure the string with later, such as a ruler or tape measure. The string will be easier to measure if the ruler is longer than the piece of string.
Wrap the string around the circle once. Loop the string around the circle and pull it tight. If you are measuring a coin or other thin object, you might not be able to pull the string tight around it. Lay the circular object flat instead and arrange the string around it, as close to it as you can get. Be careful not to wrap more than once.
You should end up with a single loop of string, so there is no part of the circle with two lengths of string next to it. Mark or cut the string. Find the place on the string that completes the loop, touching the end of the string that you started with. Mark this place with a permanent marker, or use a pair of scissors to cut it at this points.
Unravel the string and measure it with a ruler. Take the loop of string and measure it on a ruler. If you used a marker, only measure from the end of the string to the colored mark. This is the part of the string that was wrapped around the circle, and since a circle's circumference is just the distance around the circle, you've found the answer!
The length of this string is the same as the circumference of the circle. A bicycle wheel has a radius of 56 cm. How do I calculate the distance the wheel travels in five complete revolutions?
Double the radius. That's the diameter. Multiply the diameter by pi. That's the circumference. Multiply the circumference by five. That's how far the wheel travels in five revolutions. That is to say, you can find the circumference of a circle just by multiplying the diameter by pi. Plug the given value of the diameter into the formula and solve.
Check out the example problem below if you'd like extra practice. Method 2. In this formula, "r" represents the radius of the circle. Plug the given radius into the equation and solve. For this example, let's say you're cutting out a decorative strip of paper to wrap around the edge of a pie you've just made.
The radius of the pie is 5 inches. The diameter is the length of a straight line drawn through the center of a circle from one side to the other.
The circumference is the length all the way around the outside of the circle. Not Helpful 39 Helpful The perimeter of a circle is the same as its circumference, the distance around it.
Not Helpful 54 Helpful Circumference is the distance around the perimeter of a circle. It is calculated by multiplying the distance across the center diameter by Pi 3. Not Helpful Helpful Double the radius to get the diameter. Then multiply by pi to get the circumference. Not Helpful 74 Helpful The diameter is just the radius times two, so divide the diameter by two and you will have the radius of the circle!
To get the diameter of a circle take the circumference C and divide it by pi 3. Divide the circumference by pi. That's the diameter. Divide by 2. That's the radius. Square the radius, and multiply by pi. That's the area. Not Helpful 97 Helpful The diameter is twice the radius. The circumference is diameter x pi, or 2 x radius x pi. If your radius is a mixed number, turn the number into an improper fraction. To do this, simply multiply the whole number part by the denominator and add that number to the numerator.
A circle's diameter is equal to the distance across the center of the circle, and is equal to the radius times 2. So, you can convert diameter to radius by dividing the diameter by 2. For example, a circle with a diameter of 8 has a radius of 4. Pi is defined as being equal to the circumference of a circle -- the distance around that circle -- divided by its diameter.
You should know that 3. The complete value of pi can stretch for an infinite number of digits to the right of the decimal point 3. However, 3. As noted above, the circumference of a circle is the length of the line around the edge of the circle. This can be expressed as the following equation:.
To calculate circumference, then, you multiply the circle's radius by 6. Take a circle with a radius of 4 inches. Multiplying the radius by 6. So the circle's circumference is You can also calculate the area of a circle using the circle's radius.
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