18 - 24 - 30 triangle

Geometry Level 1

What is the area of a triangle with side lengths 18, 24, and 30?

216 270 244 192

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9 solutions

Cai Jialin
Aug 19, 2013

From the side lengths 18, 24, and 30, we can see that it forms the ratio of 3:4:5

Hence, we can deduce that this is a right angled triangle, with 18 and 24 forming the right angle. To find the area, we do (18*24)/2=216 and we get the answer.

Moderator note:

Good observation that the triangle is similar to a favorite 3 4 5 3-4-5 right triangle.

We can calculate that the area of the 3 4 5 3-4-5 triangle is 6. What would the area of this similar triangle be?

Sabrina Campos
Aug 23, 2013

A² = s(s-a)(s-b)(s-c) A²= (18+24+30)/2 (s-a)(s-b)(s-c) A²= 33,5 (33,5-18)(33,5-24)(33,5-30) A² = 33,5 . 15,5 . 9,5 . 3,5 A²= 46656 A= 216

Daniel Cabrales
Aug 19, 2013

Since the lengths of the triangle have a GCF not equal to 1 1 then we can reduce it by the principle of similar triangles, this would give us the "simplest" lengths of ( 9 , 12 , 15 ) (9, 12, 15) . There are several approaches you can work on, here are some:

(1) Since the lengths satisfy the pythagorean relation, a 2 + b 2 = c 2 a^{2} + b^{2} = c^{2} , we can proceed to A = ( 1 / 2 ) ( b h ) A = (1/2)(bh) with the two shorter sides be base or height.

A = ( 1 / 2 ) ( 9 ) ( 12 ) A = (1/2)(9)(12) A = 54 A = 54 and since the side ratio of the original triangle and the simplest triangle, the ratios of their areas is equal to its square, thus,

A = 54 ( 4 ) = 216 A = 54(4) = 216

(2) Since we were given lengths of sides of the triangle, we can use Heron's Formula: A = ( s ) ( s a ) ( s b ) ( s c ) A = \sqrt{(s)(s - a)(s - b)(s - c)} where s s is the semi perimeter of the triangle.

s = ( 1 / 2 ) ( 18 + 24 + 30 ) s = (1/2)(18 + 24+ 30)

s = 9 + 12 + 15 s = 9 + 12 + 15

s = 36 s = 36

Thus,

A = ( 36 ) ( 36 18 ) ( 36 24 ) ( 36 30 ) A = \sqrt{(36)(36 - 18)(36 - 24)(36 - 30)}

A = 6 6 A = \sqrt{6^{6}}

A = 216 A = 216

Which agrees with (1).

I committed some errors, on ( 9 , 12 , 15 ) (9,12, 15) sorry about that.

Daniel Cabrales - 7 years, 9 months ago

a=18,b=24,c=30 Area=Sqrt[s(s-a)(s-b)(s-c) where 2s=a+b+c s=36, s-a=18, s-b=12, s-c=6 Area= sqrt[36x18x12x6]= sqrt[6x6x6x3x6x2x6]=6x6x6=216

Eric Brian Anil
Oct 5, 2014

we can do it by either the herons formula or the simple formula... both ways, the area is 216

Kishlaya Jaiswal
Sep 20, 2013

Clearly 2 4 2 + 1 8 2 = 3 0 2 24^2+18^2=30^2

Hence it is a Right-angled Triangle

So, Area = 1 2 × b a s e × h e i g h t = 1 2 × 18 × 24 = 216 \frac{1}{2}\times base\times height = \frac{1}{2}\times 18\times 24 = 216

Basem Hesham
Aug 20, 2013

18 , 24 , 30 is a triangle , then by divide all by 6 we get 3 , 4 , 5 as we know these lengths belong to Right-angled triangle , then area of that triangle will be ( 1/2 * 24 ) * 18 = 216 answer is = 216

Deepankar Jangid
Aug 20, 2013

by heorn's formula :_ [s(s-a)(s-b)(s-c)]^1/2 we get

semi perimeter (S):_ a+b+c/2 (where a,b,c are lengths of sides of triangle)

30+18+24/2= 36

by the heron's formula :- put the value of s 'a'b'c

area of triangle is :_ [36(36-18)(36-24)(36-30)]^1/2 = 216

there are 3 sides given in the triangle so we will find the area by Heron's Formula . Let a=18 , b=24 , c=30, S = a+b+c / 2 = 18+24+30 / 2 = 36 Area = \sqrt{s(s-a)(s-b)(s-c)} =\sqrt{36(36-18)(36-24)(36-30)} =\sqrt{36 * 18 * 12 * 6} =\sqrt{46656} =216

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