Another triangle

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DanishDynamite
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Joined: Mon Jun 07, 2004 4:58 pm
Location: Copenhagen

Another triangle

Post by DanishDynamite »

Given a right-angled triangle with the two sides of length 1, what is the shortest segment which divides this triangle into two figures with equal area?
shemp
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Location: Planet X

Re: Another triangle

Post by shemp »

DanishDynamite wrote:Given a right-angled triangle with the two sides of length 1, what is the shortest segment which divides this triangle into two figures with equal area?
Call the hypotenuse "z".

1^2 + 1^2 = z^2

2 = z^2

(sq rt)2 = z

Call the segment "a".

a^2 + (z/2)^2 = 1

a^2 + ([(sq rt)2]/2)^2 = 1

a^2 + (2/4) = 1

a^2 = 1 - .5

a^2 = .5

a = (sq rt).5

So the shortest segment is the square root of 1/2.
DanishDynamite
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Joined: Mon Jun 07, 2004 4:58 pm
Location: Copenhagen

Post by DanishDynamite »

Sorry shemp. Though you've correctly calculated the length of the segment bisecting the right-angle, this isn't the shortest segment possible.
shemp
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Joined: Thu Jun 10, 2004 12:16 pm
Title: inbred shit-for-brains
Location: Planet X

Post by shemp »

DanishDynamite wrote:Sorry shemp. Though you've correctly calculated the length of the segment bisecting the right-angle, this isn't the shortest segment possible.
Yes, I realized that was possible when I woke up this morning. I knew it seemed too easy.
millirem
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Joined: Sun Aug 29, 2004 3:51 am

Re: Another triangle

Post by millirem »

DanishDynamite wrote:Given a right-angled triangle with the two sides of length 1, what is the shortest segment which divides this triangle into two figures with equal area?
Length of segment is sqrt [sqrt(2) - 1], which is approximately 0.64359

(Let the original triangle be ABC, with A = 45 degrees and B = 90 degrees. The searched segment cuts off a triangle AB'C'; a function with this segment B'C' and another side AB' as variables can be constructed, and then the minimum of the segment is determined, using derivatives.)
ceptimus
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Post by ceptimus »

I worked out the same solution as millirem. I might as well post it, now that I've made a diagram.

The area of the original triangle is 1/2. In the diagram, I've added a line of length b, making both of the angles marked with a dot 67.5 degrees.

<img src="http://www.mround.pwp.blueyonder.co.uk/ ... angle3.gif" width="215" height="235" alt="triangle diagram" title="triangle diagram">

To divide the big triangle into two equal areas, the length of the line is:

b = sqrt(tan(45 / 2)) = 0.64359

I didn't use any calculus. I just figured that the isosceles triangle was the way to go, and used a bit of trigonometry.
<BR>
DanishDynamite
Posts: 2608
Joined: Mon Jun 07, 2004 4:58 pm
Location: Copenhagen

Post by DanishDynamite »

Well done, millirem and ceptimus!