# Thread: question for "find the coordinates of the centroid "

1. ## question for "find the coordinates of the centroid "

::: find the coordinates of the centroid of each triangle with given vertices.

A(-1,11) B(3,1) C(7,6)

how can i find it?? what formula can i use for this ?
thanks.

2. Wikipedia has a nice article on centroids which contains the solution to your type of problem:

Centroid - Wikipedia, the free encyclopedia

3. Originally Posted by sarahhh
::: find the coordinates of the centroid of each triangle with given vertices.

A(-1,11) B(3,1) C(7,6)

how can i find it?? what formula can i use for this ?
thanks.
First, use mid-point theorem to find the mid-points (X, Y, Z) of each side of triangle. For example, mid-point of AB:
$\displaystyle x = \frac{3 + (-1)}{2}$ = 1
$\displaystyle y = \frac{1 + 11}{2} = 6$
hence mid-point X = (1, 6)

Then use points X(1,6) and C(7,6) to work out the equation for line XC:
$\displaystyle \frac{y - 6}{x - 1} = \frac{6 - 6}{7 - 1}$
and simplify it into the form of
Ax + By + C = 0 or
y = mx + c
where A, B, C, m and c are positive/negative constants or coefficients.

do the same for AZ and BY, and finally put all the three equations for XC, AZ and BY together and solve it for the values of x and y, which are the coordinates of the centriod O.