Answer:
centroid (2, 2.666666666...)
circumcenter (2, 1.75)
orthocenter (2, 2.5)
Explanation:
the coordinates of the centroid of a triangle are
((x1 + x2 + x3)/3, (y1 + y2 + y3)/3)
so, we have
(-4 + 2 + 8)/3 = 6/3 = 2 = x
(0 + 8 + 0)/3 = 8/3 = y = 2.666666666...
the circumcenter is the crossing point of the lines going perpendicular through the midpoint of each side.
the orthocenter is the crossing point of the lines going perpendicular on each side through the opposing vertices (the heights of the triangle).
so, we need to calculate additionally the slopes of 2 sides and their midpoints before we can get these 2 centers. the third side would only confirm the result but not provide additional information.
A = (-4, 0), B = (2, 8), C = (8, 0)
midpoint D of AC = ((-4 + 8)/2, (0+0)/2) = (2, 0)
the slope of AC is
(y2 - y1)/(x2 - x1) = (0 - 0)/(8 - -4) = 0/12 = 0 (a flat line)
the slope of the perpendicular line is -1/slope of original line. which is -1/0 = -infinity.
but don't worry, that means it is a constant line x = ...
and since it has to go through the midpoint D, the perpendicular line is x = 2
midpoint E of BC = ((2+8)/2, (8+0)/2) = (5, 4)
the slope of BC is
(0-8)/(8-2) = -8/6 = -4/3
so, the slope of the perpendicular line is 3/4.
that line is then y = 3/4 x + b
it has to go through the midpoint E
4 = 3/4 × 5 + b = 15/4 + b
16 = 15 + 4b
4b = 1
b = 1/4
so, the full perpendicular line is
y = 3/4 x + 1/4
crossing both perpendicular lines is simply using the first in the second equation :
y = 3/4 × 2 + 1/4 = 6/4 + 1/4 = 7/4 = 1.75
for the orthocenter we can use the same slopes, but the lines go now through the opposing vertices instead through the side midpoints.
so, line 1 is going through B, which makes it also x = 2.
line 2 is going through A, so
0 = 3/4 × -4 + b
0 = -1 + b
b = 1
line 2 is then
y = 3/4 x + 1
crossing these 2 lines gives us
y = 3/4 × 2 + 1 = 6/4 + 4/4 = 10/4 = 5/2 = 2.5