Area=Perimeter? Recalling Pythagoras

Find the sum of the areas of the pythagorean triangles whose areas are equal to their perimeters

Details and Assumptions

A pythagorean triangle is the triangle in which the sides a , b , c , a,b,c, are pythagorean triple. Means a 2 + b 2 = c 2 a^2+b^2=c^2


The answer is 54.

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2 solutions

Kalpok Guha
Mar 26, 2015

Let x , y , z x,y,z are the sides of the triangle

We know two equations

x 2 + y 2 = z 2 x^2+y^2=z^2

x + y + z = 1 2 x y x+y+z=\frac{1}{2}xy

From the second equation we get

z = 1 2 x y ( x + y ) z=\frac{1}{2}xy-(x+y)

Putting the value of x x on the first we get

x 2 + y 2 = [ 1 2 x y ( x + y ) ] 2 x^2+y^2=[\frac{1}{2}xy-(x+y)]^2

or, x y 4 ( x + y ) + 8 = 0 xy-4(x+y)+8=0

or, x y 4 ( x + y ) + 16 = 8 xy-4(x+y)+16=8

or ( x 4 ) ( y 4 ) = 8 (x-4)(y-4)=8

From this we get the two triplets 6 , 8 , 10 6, 8, 10 and 5 , 12 , 13 5,12,13

So the answer is 24 + 30 = 54 24+30=\boxed{54}

Up voted. It would be better if there was explanation for how 6,8,10......and.....5,12,13 is obtain.
I give it for those who can not understand. I n t e r m s o f i n t e g e r s , ( x 4 ) ( y 4 ) = 1 8..... x 4 = 1 , a n d y 4 = 8. ( x 4 ) ( y 4 ) = 2 4..... x 4 = 2 , a n d y 4 = 4. In~terms~of~integers,~(x-4)(y-4)=1*8.....x-4=1,~~and~~y-4=8.\\ (x-4)(y-4)=2*4... ..x-4=2,~~and~~y-4=4.

Niranjan Khanderia - 3 years, 1 month ago
Vaibhav Prasad
Mar 25, 2015

Only two Pythagorean triples have perimeter equal to area :

6 , 8 , 10 6, 8, 10 and 5 , 12 , 13 5,12,13

Thus 24 + 30 = 54 24 + 30 = 54

How do you know the other triples doesn't work?

Pi Han Goh - 6 years, 2 months ago

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3 , 4 , 5 3,4,5 does not

The triples with greater numbers will form an area too large compared to the perimeter

Vaibhav Prasad - 6 years, 2 months ago

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You did proof by exhaustion on an infinite number of triplets?

Pi Han Goh - 6 years, 2 months ago

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@Pi Han Goh What are you talking about ????? what exhaustion ????? I don't understand ?

Vaibhav Prasad - 6 years, 2 months ago

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@Pi Han Goh I get it now

but i did not use it

Vaibhav Prasad - 6 years, 2 months ago

@Pi Han Goh Who's this "white rabbit" that you've asked us to follow ?

A Former Brilliant Member - 6 years, 2 months ago

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@Pi Han Goh Oh , I see . Matrix !

A Former Brilliant Member - 6 years, 2 months ago

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