A geometry problem by Swapan Bagchi

Geometry Level 1

Is the given triangle possible?

If 'yes' enter the area of the given triangle or if 'no' then
enter 0 and also explain your reasoning to the same in discussions.


The answer is 0.

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5 solutions

Ahmad Saad
May 24, 2016

Sam Bealing
May 22, 2016

Let the sides of the triangle be x x and y y . By considering the area of the triangle we get:

x y 2 = 10 × 6 2 x y = 60 \dfrac{xy}{2}=\dfrac{10 \times 6}{2} \Rightarrow xy=60

Also because the triangle is right-angled we have:

x 2 + y 2 = 1 0 2 x 2 + y 2 = 100 x^2+y^2=10^2 \Rightarrow x^2+y^2=100

Now by GM-QM inequality we have:

x y x 2 + y 2 2 \sqrt{xy} \leq \sqrt{\dfrac{x^2+y^2}{2}}

Putting in our values for x y xy and x 2 + y 2 x^2+y^2 we get:

60 100 2 60 50 60 50 \sqrt{60} \leq \sqrt{\dfrac{100}{2}} \Rightarrow \sqrt{60} \leq \sqrt{50} \Rightarrow 60 \leq 50

This is clearly a contradiction so no such triangle exists.

Moderator note:

Well explained.

Aniruddha Bagchi
May 22, 2016

Tom Engelsman
Sep 9, 2020

If we divide the hypothenuse into lengths of x x and 10 x 10-x , then by Geometric Means:

6 x = 10 x 6 36 = x 2 + 10 x x 2 10 x + 36 = 0 x = 10 ± 1 0 2 4 ( 1 ) ( 36 ) 2 = 10 ± 44 2 x = 5 ± 11 i \frac{6}{x} = \frac{10-x}{6} \Rightarrow 36 = -x^2 + 10x \Rightarrow x^2 -10x + 36 = 0 \Rightarrow x = \frac{10 \pm \sqrt{10^2 - 4(1)(36)}}{2} = \frac{10 \pm \sqrt{-44}}{2} \Rightarrow \boxed{x = 5 \pm \sqrt{11}i}

which means this right triangle configuration is impossible since x ( 0 , 10 ) x \notin (0, 10) .

Q . E . D . \mathbb{Q.} \mathbb{E.} \mathbb{D.}

Hana Wehbi
May 22, 2016

If a right triangle has a hypotenuse of 10, it means the other sides should be 6 and 8. Thus, the area should be 24. with the given dimensions of the altitude and the hypotenuse the area is 30.

Hana , if the hypotenuse is 10 it means that perp.^2 + base^2 should be 100 . In this case there are not only 6 and 8 but also pairs like 91 \sqrt{91} , 3 or 45 \sqrt{45} , 55 \sqrt{55} and so on. It need not necessarily be 6, 8.

Aniruddha Bagchi - 5 years ago

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ok, I saw your solution, I am going to dig into it, see what you did.

Hana Wehbi - 5 years ago

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