Triangle Ratios

Geometry Level 1

Let A A be the area of a triangle of side lengths 5 5 , 5 5 and 6 6 and let B B be the area of a triangle of side lengths 5 5 , 5 5 and 8 8 . What is A / B A/B ?


The answer is 1.0.

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13 solutions

Sam Cheung
Jul 19, 2014

Cutting them in half, you get two 3,4,5 triangles (pythagorean triple).

No need for Heron's Formula.

I applied Heron's Formula and then divided

Saransh Katariya - 6 years, 10 months ago

great solution

Ky Nam Nguyen - 6 years, 10 months ago

Brilliant solution. I thought of Heron's Formula just like in instance after I finish read the problem. Don't even think about cutting them in half.

Vicky Andrew - 6 years, 9 months ago

I also tried the Heron's formula but, everytime I divide it, the result is always 1.6

Ranz Roy Flores - 6 years, 8 months ago

I applied the Heron's formula and got an answer 1.1!! It's correct if approximated,, right??

Alice Harrow - 6 years, 10 months ago

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You don't need to approximate or even use Heron's formula.

Cut each triangle along the lines of symmetry and for both you get two right angled triangles with sides 3,4,5 (by pythagoras).

This means that the areas are the same, which means that the areas of A/B=1 exactly.

Sam Cheung - 6 years, 10 months ago

i also used herons formula nd got ri8 answer

Anamaya Sharma - 6 years, 10 months ago

By Heron's formula, you will get exactly 1.

Sudo Jarvis - 6 years, 10 months ago

I did not understand the question

Pavan Pc pavi - 6 years, 10 months ago
Devendra Marghade
Jul 19, 2014

Height of 1st triangle(With area A)=Sqrt(5^2-3^2)=4

Height of 2nd triangle(With area B)=Sqrt(5^2-4^2)=3

Area A/ Area B = [(1/2)x6x4 ]/[(1/2)x8x3]= 1

Amed Lolo
Feb 24, 2016

in∆{5,5,6} call angle between side 5&6 : t so cos(t)=5^2+6^2-5^2(2×5×6)=.6 so sin(t)=.8 so area of ∆=1\2×5×6×.8=12, similarly in∆{5,5,8}. cos angle between 5&8=.8 so sin=.6 so area of∆=.5×5×8×.6=12. ratio =12\12=1####

Irtaza Sheikh
Apr 17, 2015

Heros formula very easily...
S=a+b+c/2 s=8 s=9. put in it u ll get A=12 B=12 12/12= 1 Ans

Anna Anant
Dec 21, 2014

1 its very simple................. AREA OF THE RED ONE(by Heron's Formula):- SIDES =5,5 and 6 and semi-perimeter=5+5+6/2=16/2=8 HERON'S FORMULA=√ s(s-a)(s-b)(s-c), where s=semi-perimeter, a,b,c are sides and so by substituting the values we get √8(8-5)(8-5)(8-6)=√8 3 3*2= √144=12(A)........ AND BY THE PROCESS WE CAN GET THE AREA OF THE BLUE TRIANGLE WHICH WILL BE ALSO = 12(B) SO A/B = 12/12=1 ANSWER....................

just go with phytagorean. The A got 4 wether the B got 3 in height. A= 0.5 x 6 x 4 = 12; B= 0.5 x 8 x 3 = 12; A/B=12/12=1.0

Divyansh Khatri
Nov 17, 2014

Herons formula is applicable in this question

Esha Aslam
Oct 4, 2014

for area A, find S= (a+b+c)/2= (5+5+6)/2=8 by using hero's formula AREA(A)=12 for area B, find S= (a+b+c)/2= (5+5+8)/2=9 AREA (B)= 12 => A//B= 1

Hon Ming Rou
Sep 7, 2014

4*6/2 = 12

3*8/2 = 12

12/12 = 1

Akshit Bountra
Aug 3, 2014

heron's formula is also applicable directly

Here's another solution (without Heron's formula) Let A the base of the isoceles, and B be the another side. Cut each triangle into two. Then you can easily compute cos(t) for the oposite angle to the hypotenusa by cos ( t ) = A / 2 B \cos{ (t) }=A/2B

Using ( sin x ) 2 + ( cos x ) 2 = 1 { (\sin{x}) }^{2} + { (\cos{x}) }^{2} = 1 you can write sin ( t ) = ( 1 A / 2 B 2 ) 1 / 2 \sin{ (t) }= {( 1 - {A/2B}^{2} )}^{1/2}

And the area of a triangle is B sin t A / 2 B*\sin{t}*A/2

If you do this with each triangle you'll find that the ratio between the surfice of both triangles is actually 1

I though that the 5,8,8 triangle was bigger but maths never lie lol

Esrael Santillan
Jul 22, 2014

I just felt both triangles have the same area so I answered 1 and got it right. :D This question feels like a typical optical illusion question where you are asked which is bigger. And the answer is always both objects are equal.

Using Herons Formula we see that both triangles have area 12 12 therefore the answer is 1 \boxed1\; .

While this is correct, a more “Why is this true?" answer is that both are two 3-4-5 triangles put together

Aadil Bhore - 6 years, 10 months ago

I was scared that I was doing something wrong because decimals were accepted..

Justin Wong - 6 years, 10 months ago

S=(a+b+c)÷2 area=(s (s-a)(s-b)(s-c))^0.5

Rahul Allam - 6 years, 11 months ago

Very simple application of S.O.T

Kïñshük Sïñgh - 6 years, 11 months ago

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S.O.T matlab ?

Gaurav Jee - 6 years, 10 months ago

Kitbiuy formula is more useful than herons formula.

Meet chaudhari - 6 years, 10 months ago

Warning: diagram not to scale ;D

Daniel Liu - 6 years, 10 months ago

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