SAT Math Help » Geometry » Plane Geometry » Circles » Radius » How to find circumference

If a circle has an area of , what is the circumference of the circle?    Explanation:

The formula for the area of a circle is πr2. For this particular circle, the area is 81π, so 81π = πr2. Divide both sides by π and we are left with r2=81. Take the square root of both sides to find r=9. The formula for the circumference of the circle is 2πr = 2π(9) = 18π. The correct answer is 18π.

You are watching: Find the circumference of a circle whose area is

Explanation:

The formula for the area of a circle is πr2.

We are given the area, and by substitution we know that 13π πr2.

We divide out the π and are left with 13 = r2.

We take the square root of r to find that r = √13.

We find the circumference of the circle with the formula = 2πr.

We then plug in our values to find = 2√13π.

Explanation:

First you must draw the diagram. The diagonal of the rectangle is also the diameter of the circle. The diagonal is the hypotenuse of a multiple of 2 of a 3,4,5 triangle, and therefore is 10. Circumference = π * diameter = 10π.

A gardener wants to build a fence around their garden shown below. How many feet of fencing will they need, if the length of the rectangular side is 12 and the width is 8?

Explanation:

The shape of the garden consists of a rectangle and two semi-circles. Since they are building a fence we need to find the perimeter. The perimeter of the length of the rectangle is 24. The perimeter or circumference of the circle can be found using the equation C=2π(r), where r= the radius of the circle. Since we have two semi-circles we can find the circumference of one whole circle with a radius of 4, which would be 8π.

The diameter of a circle is defined by the two points (2,5) and (4,6). What is the circumference of this circle?

Explanation:

We first must calculate the distance between these two points. Recall that the distance formula is:√((x2 - x1)2 + (y2 - y1)2)

For us, it is therefore: √((4 - 2)2 + (6 - 5)2) = √((2)2 + (1)2) = √(4 + 1) = √5

If d = √5, the circumference of our circle is πd, or π√5.

A car tire has a radius of 18 inches. When the tire has made 200 revolutions, how far has the car gone in feet?

Explanation:

If the radius is 18 inches, the diameter is 3 feet. The circumference of the tire is therefore 3π by C=d(π). After 200 revolutions, the tire and car have gone 3π x 200 = 600π feet.

Explanation:

To solve, simply use the formula for the circumference of a circle. Thus, Like the prior question, it is important to think about dimensions if you don"t remember the exact formula. Circumference is 1 dimensional, so it makes sense that the variable is not squared as cubed. If you rather, you can use the following formula, but realize by defining diameter, it equals the prior one.  Thus, Explanation:

First, let"s find the radius r of the circle by using the given area.   Now, plug this radius into the formula for a circle"s circumference. The surface area of a sphere is . is a point on the surface of the sphere; is the point on the sphere farthest from . A curve is drawn from to entirely on the surface of the sphere. Give the length of the shortest possible curve fitting this description.

Explanation:

Below is a sphere with its center and with points and as described.

See more: Clue: City Where Galileo Taught Crossword Clue, Clue: City Where Galileo Taught For and to be on the surface of the sphere and to be a maximum distance apart, they must be endpoints of a diameter of the sphere. The shortest curve connecting them that is entirely on the surface is a semicircle whose radius coincides with that of the sphere. Therefore, first find the radius of the sphere using the surface area formula Setting and solving for :    The length of the curve is half the circumference of a circle with radius 10, or Substituting 10 for , this is .

Report an Error
← Previous 1 2 Next →
View SAT Mathematics Tutors
Bejoy Certified Tutor
Fordham University, Bachelor in Arts, Biology, General. Iona College, Master of Science, Adolescent Math Teaching.
View SAT Mathematics Tutors
Patricia Certified Tutor
Hofstra University, Bachelor in Arts, Clinical Psychology. CUNY Hunter College, Master of Science, Dance Therapy.
View SAT Mathematics Tutors
Phoebe Certified Tutor
University of California-Irvine, Bachelor in Arts, Ecology. National University, Master of Science, Ecommerce.

### All SAT Math Resources

16 Diagnostic Tests 660 Practice Tests Question of the Day Flashcards Learn by Concept
SAT Math Tutoring in Top Cities:
Atlanta SAT Math Tutoring, Austin SAT Math Tutoring, Boston SAT Math Tutoring, Chicago SAT Math Tutoring, Dallas Fort Worth SAT Math Tutoring, Denver SAT Math Tutoring, Houston SAT Math Tutoring, Kansas City SAT Math Tutoring, Los Angeles SAT Math Tutoring, Miami SAT Math Tutoring, New York City SAT Math Tutoring, Philadelphia SAT Math Tutoring, Phoenix SAT Math Tutoring, San Diego SAT Math Tutoring, San Francisco-Bay Area SAT Math Tutoring, Seattle SAT Math Tutoring, St. Louis SAT Math Tutoring, Tucson SAT Math Tutoring, Washington DC SAT Math Tutoring
SAT Math Tutors in Top Cities:
Atlanta SAT Math Tutors, Austin SAT Math Tutors, Boston SAT Math Tutors, Chicago SAT Math Tutors, Dallas Fort Worth SAT Math Tutors, Denver SAT Math Tutors, Houston SAT Math Tutors, Kansas City SAT Math Tutors, Los Angeles SAT Math Tutors, Miami SAT Math Tutors, New York City SAT Math Tutors, Philadelphia SAT Math Tutors, Phoenix SAT Math Tutors, San Diego SAT Math Tutors, San Francisco-Bay Area SAT Math Tutors, Seattle SAT Math Tutors, St. Louis SAT Math Tutors, Tucson SAT Math Tutors, Washington DC SAT Math Tutors
Popular Courses & Classes
SSAT Courses & Classes in Philadelphia, GMAT Courses & Classes in Atlanta, LSAT Courses & Classes in San Diego, SAT Courses & Classes in San Diego, MCAT Courses & Classes in Boston, SSAT Courses & Classes in Dallas Fort Worth, SSAT Courses & Classes in San Diego, GRE Courses & Classes in Dallas Fort Worth, MCAT Courses & Classes in Dallas Fort Worth, SAT Courses & Classes in Chicago
Popular Test Prep
GMAT Test Prep in Dallas Fort Worth, MCAT Test Prep in Phoenix, LSAT Test Prep in Boston, SSAT Test Prep in Denver, LSAT Test Prep in Los Angeles, SSAT Test Prep in San Diego, GMAT Test Prep in Chicago, SAT Test Prep in Denver, SAT Test Prep in Phoenix, LSAT Test Prep in Atlanta
Report an issue with this question

If you"ve found an issue with this question, please let us know. With the help of the community we can continue to improve our educational resources.

Do not fill in this field