Question 253208
Let A, B, and C be the verticies of the triangle.
By definition of midpoint, let 
(A+B)/2 = m1
(A+C)/2 = m2
(B+C)/2 = m3,
where m1, m1, m3 are midpoints that I assume are given.
Solving using a process called Gauss-Jordan Elimination, we get
Coordinate A = m1 + m2 - m3
Coordinate B = m1 - m2 + m3
Coordinate C = -m1 + m2 + m3.
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EX: m1 =  (0,2), m2 = (3,0), m3 = (3,2)
A = (0,2) + (3,0) - (3,2) = (0,0)
B = (0,2) - (3,0) + (3,2) = (0,4)
C = -(0,2) + (3,0) + (3,2) = (6,0)
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The three verticies are: (0,0) (6,0) (0,4).