2. If (5, k) is the midpoint of (2, 3) and (8, 9), then k = ?
A6
B12
C5
D7
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Answer: A) 6
k = (3 + 9)/2 = 12/2 = 6.
3. In quadrilateral ABCD the diagonals AC and BD bisect each other. A school project asks: if A(1, 2), C(7, 8), and the midpoint of BD must equal the midpoint of AC, find that common midpoint.
A(4, 5)
B(8, 10)
C(3, 4)
D(4, 4)
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Answer: A) (4, 5)
Midpoint of AC = ((1+7)/2, (2+8)/2) = (4, 5). Diagonals of a parallelogram bisect each other, so BD has the same midpoint.
4. Three collinear points lie on a line so that B is the midpoint of AC. If A(2, 5) and B(6, 9), find C.
A(10, 13)
B(4, 7)
C(8, 14)
D(10, 14)
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Answer: A) (10, 13)
C = (2*6 - 2, 2*9 - 5) = (12-2, 18-5) = (10, 13).
5. A(0, 0), B(6, 0), C(6, 8), D(0, 8) is a rectangular field. Posts are at the midpoints of AB, BC, CD, DA. A diagonal rope is tied from the midpoint of AB to the midpoint of CD. Find the length of this rope.
A16
B7
C8
D9
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Answer: C) 8
Midpoint of AB = (3, 0); midpoint of CD = (3, 8). Length = (3−3)2+(8−0)2=64=8.