Weird Triangle

Geometry Level 2

A triangle has sides 15, 41, and 52. What is its area?


The answer is 234.

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14 solutions

Hanissa S
Dec 22, 2013

By Heron's Formula we have the area of triangle as s ( s a ) ( s b ) ( s c ) \sqrt {s(s-a)(s-b)(s-c)} where a , b , c a,b,c are the side lengths and s s is the semi-perimeter which is equal to 15 + 41 + 52 2 \frac{15+41+52}{2} in this case. Plugging in the values gives us 54 ( 54 15 ) ( 54 41 ) ( 54 52 ) = 234 \sqrt {54(54-15)(54-41)(54-52)}=\boxed {234}

I did it with the cosine and sine rule, but the answer is the same anyways

Armughan Aslam - 7 years, 5 months ago

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haha me too :) But Heron's formula is faster :)

Happy Melodies - 7 years, 5 months ago

pythagorean theorem Try it. Do an altitude to the 52 side.

Bob Yang - 7 years, 5 months ago

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I used the pythagorean theorem but it still didnot work.I am not sure can you show it to me.

Mardokay Mosazghi - 7 years, 4 months ago

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@Mardokay Mosazghi The reason you guys couldn't use the pythagorean theorem was because this triangle is not a right triangle.

In this case, using Heron's Formula would be the easiest way to go (For me at least), and using cosine and sine laws is correct also.

Cameron Wong - 7 years, 4 months ago

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@Cameron Wong That triangle was an obtuse triangle but splitting it into two right triangles was the method.

Bob Yang - 7 years, 4 months ago

@Mardokay Mosazghi this works only with right triangles use herons formula instead

sujoy purkayastha - 7 years, 4 months ago

Hahaha! That #Heron'sFormula was misleading. Just split the triangle into 9, 12, 15 and 9, 40, 41 triangles.

Bob Yang - 7 years, 5 months ago

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Yep, that is one way to do it. However, it takes quite a bit of imagination to find that, so Heron's Formula would actually be much faster.

Daniel Liu - 7 years, 5 months ago

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No i think finding out the 2 triangles would be faster. Too much tedious calculation when one can see the 2 triangles. I thought there was probably a trick and found out the two triangles

Vinayak Kumar - 7 years, 5 months ago

but herons is still a viable option in solving this question

sujoy purkayastha - 7 years, 4 months ago

Much easier than my contorted solution.

Dorian Thiessen - 7 years, 1 month ago
Pavithra Pavi
Dec 23, 2013

Area=sqrt(s(s-a)(s-b)(s-c)) ; s=(a+b+c)/2 a=15,b=41,c=52 and s=54 ; Area=sqrt(54(54-15)(54-41)(54-52)) Area=sqrt(54(39)(13)(2)) Area=sqrt(54756) Area=234

Please look at the formatting guide to see how to format math.

Kartikay Kumar - 7 years, 5 months ago

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Or you can see this post of Daniel Liu: Beginner LaTeX Guide

Jorge Tipe - 7 years, 5 months ago
Vladimir Staver
Dec 23, 2013

The area formula for every triangle is known and is A = h e i g h t b a s e 2 A=\dfrac{height*base}{2} . So, first of all there is necessary to calculate the height of the triangle, for that we write the next two equations system: ( 52 x ) 2 + ( h ) 2 = ( 41 ) 2 ; ( x ) 2 + ( h ) 2 = ( 15 ) 2 (52-x)^2+(h)^2=(41)^2; (x)^2+(h)^2=(15)^2 . Now we procede to calculate the systems equations by the reduction method: ( 52 x ) 2 + ( h ) 2 = ( 41 ) 2 (52-x)^2+(h)^2=(41)^2 . ( x ) 2 ( h ) 2 = ( 15 ) 2 ( 52 x ) 2 ( x ) 2 = ( 41 ) 2 ( 15 ) 2 ( 52 ) 2 2 52 x + ( x ) 2 ( x ) 2 = 1681 225 = 1456 2 52 x = 1456 ( 52 ) 2 = 1248 x = 1248 / 2 52 = 12 -(x)^2-(h)^2=-(15)^2 \\ (52-x)^2- (x)^2=(41)^2-(15)^2 \\ \Rightarrow (52)^2-2*52*x+(x)^2 -(x)^2 \\ =1681-225 \\ =1456 \\ \Rightarrow -2*52*x=1456-(52)^2=-1248 \\ \Rightarrow x=1248/2*52=12 .

Now we substitute the x in one of the two equations to know the value of h. ( h ) 2 = ( 15 ) 2 ( 12 ) 2 = 81 h = 81 = 9 (h)^2=(15)^2-(12)^2=81 \\ \Rightarrow h=\sqrt{81}=9

Hence the area of the triangle is A = 52 9 2 = 234. A=\dfrac{52*9}{2}=234.\square

The area is S ( S a ) ( S b ) ( S c ) \sqrt{ S * (S-a) * (S-b) * (S-c) } S = ( a + b + c ) 2 S=\frac{(a+b+c)}{2} and a=15 ,b=41 and c=52

Govind Patel
Jan 24, 2014

a,b,c be the side length

p = ( a + b + c ) / 2 = ( 15 + 41 + 52 ) / 2 = 54 (a+b+c)/2\\ = (15+41+52)/2\\ = 54

Area = p × ( p a ) × ( p b ) × ( p c ) = 54 × ( 54 15 ) × ( 54 41 ) × ( 54 52 ) = 54756 = 234. \sqrt{p\times(p-a)\times(p-b)\times(p-c)}\\ = \sqrt{54\times(54-15)\times(54-41)\times(54-52)} \\ = \sqrt{54756} \\ = 234.

Prasun Biswas
Jan 5, 2014

Given sides are 15 , 41 , 52 15,41,52 . Let us take these sides as a , b , c a,b,c respectively and s s be the semi-perimeter of the triangle, i.e, half the perimeter of the triangle.

We shall use here Heron's formula which states that, Area = s ( s a ) ( s b ) ( s c ) =\sqrt{s(s-a)(s-b)(s-c)} for a triangle of sides a , b , c a,b,c and semi-perimeter s s .

Perimeter of this triangle = 15 + 41 + 52 = 108 =15+41+52=108 . So, s = 108 2 = 54 s=\frac{108}{2}=\boxed{54}

Area = 54 ( 54 15 ) ( 54 41 ) ( 54 52 ) =\sqrt{54(54-15)(54-41)(54-52)}

= 54 × 39 × 13 × 2 =\sqrt{54\times 39\times 13\times 2}

= 9 × 6 × 13 × 3 × 13 × 2 = 3 2 × 1 3 2 × 6 2 = 3 × 13 × 6 = 234 =\sqrt{9\times 6\times 13\times 3\times 13\times 2} = \sqrt{3^{2}\times 13^{2}\times 6^{2}} = 3\times 13\times 6=\boxed{234}

We can use another form of Heron's formula:

1 4 4 a 2 b 2 ( a 2 + b 2 c 2 ) 2 \frac{1}{4}\sqrt{4a^2b^2-(a^2+b^2-c^2)^2}

Which for our question can be written as:

1 4 4 1 5 2 4 1 2 ( 1 5 2 + 4 1 2 5 1 2 ) 2 \frac{1}{4}\sqrt{4*15^2*41^2-(15^2+41^2-51^2)^2}

This can be simplified to:

1 4 1512900 636804 \frac{1}{4}\sqrt{1512900-636804}

Which can be further simplified to:

1 4 876096 \frac{1}{4}\sqrt{876096}

which then equals to

1 4 936 \frac{1}{4}*936

So our answer is:

936 4 = 234 \frac{936}{4}=234

Answer:

= 234 = \boxed{234}

compute any angle by cosine law

5 2 2 = 1 5 2 + 4 1 2 2 ( 15 ) ( 41 ) c o s B 52^2 = 15^2 + 41^2 - 2(15)(41)cosB

B = 130.45 d e g r e e s B = 130.45 degrees

A A = = 1 2 \frac{1}{2} 15 41 *15*41 s i n 130.45 *sin130.45 = 234 =234

John Ray Matugas
Mar 27, 2014

First find for the semi-perimeter:

s = ( 15 + 41 + 52 ) / 2 = 54

then using Heron's Formula:

A = sq. root of (54 x (54-15) x (54 - 41) x (54 - 52)) A = 234 sq. units :)

Vivek Brahmbhatt
Feb 24, 2014

area of a scalene triangle (whose all sides are different) is given by (s(s-a)(s-b)(s-c))^0.5 where s=(a+b+c)/2, a,b,c being sides of triangle.

Lyra Lou Baldoza
Jan 14, 2014

You can USE the Heron's Formula in solving the area of a triangle (if the lengths of 3 sides are already given)

Let a, b, c be the lengths of the sides of a triangle.

Area = square root of p(p-a) (p-b) (p-c)

where "p" is half the perimeter, or:

a + b + c / 2 [[this can be understand as, "the SUM of 3 sides DIVIDED by 2"]]

This is how it goes:

a = 15

b = 41

c = 52

p = 54 [[ 15+41+52 = 108 DIVIDED BY 2]]

A = square root of 54 (54 - 15) (54 - 41) (54 - 52)

A = square root of 54 (39) (13) (2)

A = square root of 54756

Therefore, the area is 234.. :)

Krutik Desai
Jan 3, 2014

The semi-perimeter of the triangle is (15+41+52)/2 whose answer is 54.Now by heron's formulae we can derive the area easily. The heron's formulae is the square root of {s(s-a)(s-b)(s-c)} where s is the semi-perimeter and a , b and c are the sides of the triangle.

Hannan Khan
Dec 23, 2013

sol:- let a =15, b=41,c=52 S=a+b+c/2 =15+41+52/2=>54 A=(s(s-a)(s-b)(s-c))^1/2 here a is area of triangle =(54(54-15)(54-41)(54-52))^1/2 =234

Budi Utomo
Dec 22, 2013

We know if 15^2 = 12^2 + 9^2 and 41^2 = 40^2 + 9^2 ,also 40 + 12 = 52. Because it can make a triangle has side 15, 41, 52. So, the areas is (9 x 52 )/2 = 9 x 26 = 234. Answer : 234

Please look at the formatting guide to see how to format math.

Kartikay Kumar - 7 years, 5 months ago

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