Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

Area of circumscribed circle

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Source: — Problem Solving |
Legendary Member
Posts: 1578
Joined: Sun Dec 28, 2008 1:49 amFollowed by: 9 members
Thanked: 82 times
GMAT Score:720

by maihuna » Mon Aug 10, 2009 8:32 am
For any given regular polygon:

a = 2R sin(pi/n)

Here 10 = 2R sin60 = 2R*\/3/2 => R = 10/\/3

so area = PI R^2 = PI* 100/3 = 100PI/3
Charged up again to beat the beast :)
Top
Join the discussion
Master | Next Rank: 500 Posts
Posts: 435
Joined: Sat May 02, 2009 3:55 am
Thanked: 17 times

by madhur_ahuja » Mon Aug 10, 2009 8:35 am
maihuna wrote:For any given regular polygon:

a = 2R sin(pi/n)

Here 10 = 2R sin60 = 2R*\/3/2 => R = 10/\/3

so area = PI R^2 = PI* 100/3 = 100PI/3
Can you elaborate ? What does a and n signify here?
Top
Join the discussion
Legendary Member
Posts: 1578
Joined: Sun Dec 28, 2008 1:49 amFollowed by: 9 members
Thanked: 82 times
GMAT Score:720

by maihuna » Mon Aug 10, 2009 8:38 am
a will be side of polygon
n will be no of sides.
Charged up again to beat the beast :)
Top
Join the discussion
Master | Next Rank: 500 Posts
Posts: 256
Joined: Mon Aug 10, 2009 6:31 pm
Thanked: 3 times

by gmatv09 » Wed Aug 12, 2009 8:45 am
Radius of a circle circumscribing a equilateral triangle (R) = a/sqrt(3)
[Formula to remember]

R = 10/sqrt(3)

Therefore area of the circle = 100/3 * pi
Top
Join the discussion
Master | Next Rank: 500 Posts
Posts: 101
Joined: Tue Apr 07, 2009 12:30 am
Thanked: 2 times
GMAT Score:750

by Svedankae » Wed Aug 12, 2009 9:00 am
gmatv09 wrote:Radius of a circle circumscribing a equilateral triangle (R) = a/sqrt(3)
[Formula to remember]

R = 10/sqrt(3)

Therefore area of the circle = 100/3 * pi

So by that logic is the radius of a circle circumscribing a regular pentagon (R) = a/sqrt(5)

With "a" being the length of one side of the pentagon?
Top
Join the discussion
Master | Next Rank: 500 Posts
Posts: 256
Joined: Mon Aug 10, 2009 6:31 pm
Thanked: 3 times

by gmatv09 » Wed Aug 12, 2009 11:16 am
No. this formula is applicable to triangles only - AFAIK
:)
Top
Join the discussion
Legendary Member
Posts: 1578
Joined: Sun Dec 28, 2008 1:49 amFollowed by: 9 members
Thanked: 82 times
GMAT Score:720

by maihuna » Sat Aug 15, 2009 9:15 am
gmatv09 wrote:No. this formula is applicable to triangles only - AFAIK
:)
Actually this formula is applicable for all cases.
Charged up again to beat the beast :)
Top
Join the discussion
Master | Next Rank: 500 Posts
Posts: 256
Joined: Mon Aug 10, 2009 6:31 pm
Thanked: 3 times

by gmatv09 » Sat Aug 15, 2009 12:05 pm
thanks !
Top
Join the discussion
Legendary Member
Posts: 1578
Joined: Sun Dec 28, 2008 1:49 amFollowed by: 9 members
Thanked: 82 times
GMAT Score:720

by maihuna » Sat Aug 15, 2009 12:21 pm
Svedankae wrote:
gmatv09 wrote:Radius of a circle circumscribing a equilateral triangle (R) = a/sqrt(3)
[Formula to remember]

R = 10/sqrt(3)

Therefore area of the circle = 100/3 * pi

So by that logic is the radius of a circle circumscribing a regular pentagon (R) = a/sqrt(5)

With "a" being the length of one side of the pentagon?
Note this formula (yes applicable only for regular polygons)

a = 2rtan(PI/n) = 2Rsin(PI/n) where r and R has obvios meaning

for pentagon: a = 2Rsin(180/5) = 2Rsin(36) you know finding 36 will not be possible w/o a sine table, so its normally useful for 30,45,60,90 when PI/n results in such scenario.
Charged up again to beat the beast :)
Top
Join the discussion