All related to triangles Part 1

Geometry Level 2

The diagram to the right shows a triangle A B C ABC inscribed in a 6 × 8 6\times 8 rectangle.

What is the area of this triangle?


See Part 2 and Part 3 .


The answer is 14.

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8 solutions

Eamon Gupta
May 25, 2015

The area of the rectangle is 48 u n i t s 2 48units^{2} .

The triangle with hypotenuse AB has area 3 × 2 × 1 2 = 3 u n i t s 2 3\times2\times\frac{1}{2}=3units^{2} .

The triangle with hypotenuse AC has area 5 × 6 × 1 2 = 15 u n i t s 2 5\times6\times\frac{1}{2}=15units^{2} .

The triangle with hypotenuse BC has area 4 × 8 × 1 2 = 16 u n i t s 2 4\times8\times\frac{1}{2}=16units^{2} .

Then by subtracting the other triangle areas we get 48 15 16 3 = 14 u n i t s 2 48-15-16-3=\boxed{14units^{2}} .

Moderator note:

Yes, finding the area by "complement" is the easiest way to approach this problem. It would be better to explain how you get the values of 3 , 15 , 16 3,15,16 unit squared.

Addendum: Great work! Now try Part 2 and Part 3.

Just edited, thanks.

Eamon Gupta - 6 years ago

please explain how u got the sides of traingle as 3 and 2 where AB is hypotenuse.

Sagar Bagchi - 6 years ago

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Just count the squares..:P

Eamon Gupta - 6 years ago

each box is 1 unit!!

Shrey Pithava - 6 years ago

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many many thanks,you have cleared my doubts.

Sagar Bagchi - 6 years ago

Area of AB has a max of 3 rows & 2 cols

bhuvan kireeti - 6 years ago

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may many thanks.you have cleared my doubt.

Sagar Bagchi - 6 years ago

Using the Pick's formula A r e a = 12 + 6 / 2 1 = 14 Area=12+6/2-1=14

can u elaborate on pick's formula

Bharat Naik - 6 years ago
Tahmid Chowdhury
Jun 1, 2015

It can be solved by means of coordinate geometry.Along X axis and Y axis respectively A(3,6),B(0,4) and C(8,0).then using the formula for determining area in coordinate geometry which is: 0.5(x1y2+x2y3+x3y4-x2y1-x3y2-x4y3) we can determine the area of the inscribed triangle.

Shoelace formula to the rescue.

Chung Kevin - 6 years ago
Andy Brighouse
May 25, 2015

Start with the area of the rectangle, 6x8=48 then subtract the areas of the right angled triangles in the corners.

Vijay Simha
May 31, 2015

Interior points (Colored Orange = 12) -> i

Border points (Colored Green = 6) -> b

Area = i + 0.5b -1 = 12 + 3 -1 = 14

Ariel Gershon
May 31, 2015

I used the Shoelace Formula:

Suppose the points are on a Cartesian plane. Then we can represent the points as A = ( 3 , 6 ) , B = ( 0 , 4 ) , C = ( 8 , 0 ) A = (3,6), B = (0,4), C = (8,0) . Then the Shoelace formula gives us:

A r e a = 1 2 ( 3 4 6 0 ) + ( 0 0 8 4 ) + ( 8 6 0 3 ) = 14 Area = \dfrac{1}{2}\left|(3*4-6*0)+(0*0-8*4)+(8*6-0*3)\right| = 14

i simply don't have any idea... i just starred at the pic for a while and guessed area of triangle approximately occupies 30% of rectangular area. it gave me 14.4 but i answered 14... luckily that was ryt :D

Do you know why the area must be an integer, or half of an integer? If your approximation is correct, that will further tell you that the answer is 14 or 14.4 or 15!

Chung Kevin - 6 years ago
Chris Thompson
May 31, 2015

Found the hypotenuse for each triangle on the outside which gave me the insides coordinates. From there i calculated the area as if it were a rectangle. Then simply divided it by 2. Mathematics brought to you by stoner chris

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