You are not logged in.
#1 2005-09-24 03:46:21
- Michael
- Guest
geometry problem: how to determine area
Hello
I need help with a problem I found in a book called "Geometrical Puzzles". I need to determine what fractal of the area of the outer square the area of the inner square is. (See the image)
Image
Now, I do know it's in fact 1/5, but I also need to prove that. That's what I got so far: (a is the len of the outer square)
DQ² = a² + 1/2a²; DQ = √(1,5a²)
gQ = 1/5 * √(1,5a²)
hg = 2/5 * √(1,5a²)
It's no problem showing that Dh=hg=2*gQ=gf=ef=eh...using the intercept theorem.
But now, when I want to calculate the area of hg², I get instead of 1/5a² (=0,25a²) only 0,24a². That's a close miss....What the hell am I doing wrong?
Michael
#2 2005-09-24 10:42:27
- John E. Franklin
- Star Member
Offline
Re: geometry problem: how to determine area
line2: y=2x
line1: y = -x/2 + a
line3: y=2x - a
intersection lines 1 and 2 is (0.4a,0.8a)
intersection lines 1 and 3 is (0.8a,0.6a)
small square side length is square root of ((.4² + .2²)a²), which is the square root of 0.2a².
If you square the side length for the area, you get 0.2a²,
which is five times smaller than the big square's area: a².
Last edited by John E. Franklin (2005-09-24 10:48:21)
Imagine for a moment that even an earthworm may possess a love of self and a love of others.
#3 2005-09-24 20:57:40
- Michael
- Guest
Re: geometry problem: how to determine area
Oh my god, I have been stupid...posting 0,25=1/5 
Thx for your answer John, but the JPG isn't viewable (Hotlinking seems to be not allowed). You might try http://www.imageshack.us? No registration required.