area of isosceles triangle

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ketkoag: Legendary Member; Posts: 876; Joined: Thu Apr 10, 2008 8:14 am; Thanked: 13 times

area of isosceles triangle

by ketkoag » Tue Jul 07, 2009 11:56 pm

Guys, please lemme know how to calculate the area of an isosceles triangle if two of its sides and one angle are given. None of the angles are right angle.. I came across such question a few days back but can't remember it now..
Please help me with this; how to solve it or any standard formula for the same?

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Source: Beat The GMAT — Problem Solving | Tue Jul 07, 2009 11:56 pm

Musiq: Senior | Next Rank: 100 Posts; Posts: 93; Joined: Thu Apr 10, 2008 1:42 pm; Location: Chicago; Thanked: 20 times

Re: area of isosceles triangle

by Musiq » Wed Jul 08, 2009 9:10 am

ketkoag wrote:Guys, please lemme know how to calculate the area of an isosceles triangle if two of its sides and one angle are given. None of the angles are right angle.. I came across such question a few days back but can't remember it now..
Please help me with this; how to solve it or any standard formula for the same?

Hi Ket, can you provide some numbers?

There could be some ways to solve this problem in a GMAT context, but having the value of the angle and the sides helps.

Sincerely,
Musiq

For love, not money.

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Morgoth: Master | Next Rank: 500 Posts; Posts: 316; Joined: Mon Sep 22, 2008 12:04 am; Thanked: 36 times; Followed by:1 members

by Morgoth » Thu Jul 09, 2009 4:22 am

Area of an isosceles triangle = b/4 *[sqrt(4a^2 -b^2)]

Height of an isosceles triangle = 1/2 *[sqrt(4a^2 -b^2)]

b = base

a = one of the equal sides

Hope this helps.

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pm; Location: Toronto; Thanked: 1710 times; Followed by:614 members; GMAT Score:800

Re: area of isosceles triangle

by Stuart@KaplanGMAT » Thu Jul 09, 2009 11:44 am

ketkoag wrote:Guys, please lemme know how to calculate the area of an isosceles triangle if two of its sides and one angle are given. None of the angles are right angle.. I came across such question a few days back but can't remember it now..
Please help me with this; how to solve it or any standard formula for the same?

On the GMAT, you definitely do not need to know the formula above - you just need to know the pythagorean theorum (from which the formula is derived).

You also don't need to know any trigonometry, so unless the angle is 30, 60 or 45 (angles which would lead to special right triangles and shortcuts to identifying the height) it's unlikely to be relevant to your calculation; the main purpose of that angle will be to allow you to conclude which of the two sides is duplicated.