Giant triangle!

Geometry Level 4

Does there exist a triangle with all 3 altitudes summing to less than 1 meter and area bigger than the surface area of Earth, which is approximately 51 × 1 0 7 km 2 ? 51\times 10^7\text{ km}^2 ?

No, there does not Yes, there exists

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2 solutions

Michael Mendrin
Mar 29, 2017

Let an isosceles triangle have vertices with the following coordinates

( s , 0 ) (-s,0)
( 0 , 0 ) (0,0)
( s 2 0.3 2 , 0.3 ) (\sqrt{{s}^{2}-{0.3}^{2}}, 0.3)

then the sum of the altitudes will be < 1 < 1 , while the area of the triangle will be 0.15 s 0.15s , and s s can be as large as one wants.

Linkin Duck
Mar 30, 2017

Let consider an isosceles triangle A B C ABC such that A B = b = A C = c AB=b=AC=c , B C = a = 6 × 10 14 k m BC=a=6\times { 10 }^{ 14 }km , the height from A A h a = 0.2 m m = 2 × 10 7 k m { h }_{ a }=0.2mm=2\times { 10 }^{ -7 }km . ( A A can be formed from the bisector of the given line B C BC and the given distance from A A to B C BC )

We can see that B A C ^ = α \widehat { BAC } =\alpha is very very near to 180 0 { 180 }^{ 0 } ( 179.999... 0 { 179.999... }^{ 0 } ) and the area of A B C ABC is 6 × 10 7 k m 2 ( > 5.1 × 10 7 ) 6\times { 10 }^{ 7 }{ km }^{ 2 }\quad \left( >5.1\times { 10 }^{ 7 } \right)

Since b = c > a 2 b=c>\frac { a }{ 2 } (Triangle inequality) h b = h c < 2 h a h a + h b + h c < 5 h a = 1 m m \Longrightarrow { h }_{ b }={ h }_{ c }<2{ h }_{ a }\Longrightarrow { { h }_{ a }+h }_{ b }+{ h }_{ c }<5{ h }_{ a }=1mm .

Therefore, the triangle A B C ABC above satisfies all the conditions \Longrightarrow The answer is T r u e \boxed { True } .

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