Pythagorean Triangle in Square

Geometry Level 4

Let A B C D ABCD be a square with points E E and F F on C D CD and B C , BC, respectively, such that A E E F , A E = 4 , AE \perp EF, AE=4, and E F = 3. EF=3.

If the area of A B C D ABCD can be written as a b \frac{a}{b} , where a a and b b are coprime positive integers, find the value of a + b . a+b.


The answer is 273.

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1 solution

Sharky Kesa
Nov 22, 2017

I thought this was a really nice question.

We have C E F = 9 0 D E A A E D \angle CEF = 90^{\circ} - \angle DEA - \angle AED , and A D E = E C F = 9 0 \angle ADE = \angle ECF = 90^{\circ} . Thus, Δ A D E Δ E C F \Delta ADE \sim \Delta ECF . Comparing proportional sides, we have A D A E = E C E F \frac{AD}{AE} = \frac{EC}{EF} , so A D = 4 3 E C AD = \frac{4}{3} EC , so A D = 4 D E AD = 4DE . We also have A D 2 + D E 2 = A E 2 AD^2 + DE^2 = AE^2 , so 17 D E 2 = 16 17DE^2 = 16 . Thus, D E = 4 17 DE = \frac{4}{\sqrt{17}} , so A D = 16 17 AD = \frac{16}{\sqrt{17}} . Thus, the area of the square is A D 2 = 256 17 AD^2 = \frac{256}{17} . Thus, the answer is 256 + 17 = 273 256+17 = \boxed{273} .

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