If you're experiencing a roadblock with one of the Manhattan Prep GMAT math strategy guides, help is here!
aren.sh
Forum Guests
 
Posts: 2
Joined: Thu Mar 07, 2013 9:15 am
 

What is the area of an equilateral triangle... (Geometry)

by aren.sh Tue Aug 13, 2013 6:10 pm

Guide #4, Geometry: Chapter 2 problem set question #8:

What is the area of an equilateral triangle whose sides measure 8 cm long?

Using the ratio of 1:rad3:2, I get 4:4rad3:8. So far so good with the explanation given, but when using A=base X height / 2, I plugged in 4 X 4rad3 / 2 and ended up with 8rad3.

The explanation uses 8 X 4rad3 and ends up with 16rad3. The 8 is the hypotenuse and the 4rad3 is the height, how can this be? I know the section right before it says you can choose the hypotenuse as the base, but then the height should be 4 and that would result in 8 X 4 / 2 = 16.

Really baffled how they got away using the 8 and not the 4.
RonPurewal
Students
 
Posts: 19744
Joined: Tue Aug 14, 2007 8:23 am
 

Re: What is the area of an equilateral triangle... (Geometry)

by RonPurewal Wed Aug 14, 2013 5:14 am

you're finding the area of the wrong triangle.

go back and read the problem again, and note which triangle you're supposed to find the area of.