Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**Michael****Guest**

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)

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

**John E. Franklin****Member**- Registered: 2005-08-29
- Posts: 3,562

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 (2005-09-23 12:48:21)*

**igloo** **myrtilles** **fourmis**

Offline

**Michael****Guest**

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.

Pages: **1**