What's the area?

Geometry Level 2

In triangle A B C \triangle ABC , B E BE and C F CF are medians. B E = 9 cm BE=9\text{ cm} , C F = 12 cm CF=12\text{ cm} . If B E BE is perpendicular to C F CF , find the area of the triangle A B C \triangle ABC in cm 2 \text{ cm}^2 .


The answer is 72.

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3 solutions

Paola Ramírez
Jun 21, 2015

By medians propierties C G = 8 CG=8 and B G = 6 BG=6 ). Then is known that medians divides a triangle in six triangles of equal areas \therefore area of B G C = \triangle BGC = area of A G C = \triangle AGC= area of A G B \triangle AGB ; as B G C \triangle BGC is right angle triangle with cathetus 6 6 and 8 8 its area is 6 × 8 2 = 24 \frac{6\times8}{2}=24 \Rightarrow the area of A B C = 24 × 3 = 72 \triangle ABC=24\times 3=\boxed{72}

How do you know that the triangle BGC is normal triangle?!

Adel El-ngar - 5 years, 11 months ago

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it is the given data.

Raven Herd - 5 years, 11 months ago

It was stated in the problem.

A Former Brilliant Member - 4 years, 1 month ago

What is the meaning of the close parenthesis symbol in B G = 6 BG=6 )? I think it is just a typo error.

A Former Brilliant Member - 4 years, 1 month ago

The three medians of a triangle meet in a point, the centroid, which is situated on each median so the measure of the segment from the vertex to the centroids is two-third the measure of the median. So

F O = 1 3 ( 12 ) = 4 FO=\dfrac{1}{3}(12)=4

B O = 2 3 ( 9 ) = 6 BO=\dfrac{2}{3}(9)=6

The three medians of a traingle divide the triangle into six equal areas, so the area of triangle A B C ABC is

A A B C = 6 ( 1 2 ) ( 6 ) ( 4 ) = A_{ABC}=6\left(\dfrac{1}{2}\right)(6)(4)= 72 \boxed{72}

This is my old account.

A Former Brilliant Member - 1 year, 6 months ago

Nice solution.

Marvin Kalngan - 10 months, 1 week ago
Jeffrey H.
May 11, 2019

We notice that quadrilateral FEBC is an orthogonal quadrilateral, so its area is the product of its diagonals divided by two, which is 9 12 2 = 54 \frac{9\cdot 12}{2}=54 . We then see, since points F and E are midpoints, that line segment FE is a midline. Thus, triangle AFE is one fourth of the area of the whole triangle, and so quadrilateral FEBC is three fourths the area of the whole triangle. Therefore, our answer is 4 3 54 = 72 \frac{4}{3}\cdot 54=\boxed{72} .

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