# Thread: The centroid of a triangle with coordinates

1. ## The centroid of a triangle with coordinates

Triangle DEF has vertices D(1,3) and E(6,1), and centroid at C(3,4). Determine the coordinates of point F.

I know that the medians in a triangle intersect at the centroid and that the centroid divides each median in a ration of 2:1. Also, I know that each median intersects a side at its midpoint with the shorter part of the median. What I did was find the midpoint between point E and F by taking half of the line D to C and adding onto C to give point G. The coordinates of point G was found to be (4, 4.5). Since I knew that the change in the coordinates between points E and G, (-2, 3.5), was only half of the line EF I doubled it and added it point E to give the answer (2, 8). I wanted to know if there was an easier way to do this.

2. Originally Posted by darksoulzero
Triangle DEF has vertices D(1,3) and E(6,1), and centroid at C(3,4). Determine the coordinates of point F.

I know that the medians in a triangle intersect at the centroid and that the centroid divides each median in a ration of 2:1. Also, I know that each median intersects a side at its midpoint with the shorter part of the median. What I did was find the midpoint between point E and F by taking half of the line D to C and adding onto C to give point G. The coordinates of point G was found to be (4, 4.5). Since I knew that the change in the coordinates between points E and G, (-2, 3.5), was only half of the line EF I doubled it and added it point E to give the answer (2, 8). I wanted to know if there was an easier way to do this.
Read Centroid - AoPSWiki

3. ## centroid of triangle

Hi darksoulzero,

Your solution is confusing.Here is a suggested method.

connect M midpoint of DE and C (centroid) with extended lenght.F lies on this line. FC = 2CM. Slope diagram of C and M = 2/1/2.Slope diagram of FC is twice that or 4/1. Working from point C one point left and 4 points up gives F (2,8)

bjh

4. If ABC is a triangle with $A\left( {{x_1},{y_1}} \right),B\left( {{x_2},{y_2}} \right),C\left( {{x_3},{y_3}} \right)$ then its centroid is
$G\left( {\tfrac{{{x_1} + {x_2} + {x_3}}}{3},\tfrac{{{y_1} + {y_2} + {y_3}}}{3}} \right)$

5. Hello, darksoulzero!

$\text{Triangle }D{E}F\text{ has vertices: }D(1,3)\text{ and }E(6,1)\text{, and centroid at }C(3,4).$
$\text{Determine the coordinates of point }F.$
Code:

1
F o-----+
\    :
\   :4
\  :
\ :
\:0.5
(3,4)o---+
D       C\  :
o         \ :2
(1,3)   *    \:
M o
(3.5,2)   *     E
o
(6,1)

We have vertices $D(1,3)$ and $E(6,1)$, and centroid $C(3,4).$

The midpoint of $DE$ is: $M(3\tfrac{1}{2},\,2).$

The median to side $DE$ starts at $\,M$, passes through $\,C,$
. . and extends to $\,F$, where: . $FC \,=\,2\!\cdot\!CM.$

Going from $\,M$ to $\,C$, we move up 2 and left $\frac{1}{2}$
Hence, going from $\,C$ to $\,F$, we move up 4 and left 1.

Therefore, we have: . $F(2,8).$