The mid-points of the sides of a triangle are (5, 7, 11), (0, 8, 5) and (2, 3, – 1). Find its vertices.
Given:
Mid-points of sides of triangle ABC are,
D(5,7,11), E(0,8,5) & F(2,3,-1)
Let us assume that the vertices of the triangle are –
A(x1, y1, z1), B(x2, y2, z2) & C(x3, y3, z3).
Now, we know that E is the mid-point of AC, thus,
(x1 + x3/2, y1 + y3/2, z1 + z3/2) = (0,8,5)
Thus,
C(x3, y3, z3) = C(-x1, 16 – y1, -2-z1)
Now, mid-point of AB, F is
(x1 + x2/2, y1 + y2/2, z1 + z2/2) = (2,3,-1)
Now, B(x2, y2, z2) = B(4-x1, 6-y1, -1-z1)
Now, mid-point of BC, D is,
-x1 + 4 – x1/2 = 5,
16 – y1 + 6 – y1/2 = 7
& 10 – z1 – 2 – z1/2 = 11
Thus, x1 = -3, y1 = 4 & z1 = -7
Thus, A = (-3,4,-7), B = (7,2,5) & C = (3,12,17)