Difficulty: Easy
Correct Answer: (8, 2)
Explanation:
Introduction / Context:
This problem tests the midpoint formula in coordinate geometry. If a point P is the midpoint of segment AB, then P lies exactly halfway between A and B. That means P’s x-coordinate is the average of the x-coordinates of A and B, and similarly for the y-coordinates. Many aptitude problems reverse the usual direction: instead of finding the midpoint, you are given the midpoint and one endpoint and must find the other endpoint.
Given Data / Assumptions:
Concept / Approach:
Use the midpoint formula:
Midpoint P = ((xA + xB)/2, (yA + yB)/2).
Solve two simple equations:
(xA + xB)/2 = xP and (yA + yB)/2 = yP.
Then isolate xB and yB by multiplying by 2 and subtracting the known endpoint coordinates.
Step-by-Step Solution:
1) Write the midpoint equations:
(2 + xB)/2 = 5
(-4 + yB)/2 = -1
2) Solve for xB:
2 + xB = 10
xB = 10 - 2 = 8
3) Solve for yB:
-4 + yB = -2
yB = -2 + 4 = 2
4) Therefore, point B is:
(8, 2)
Verification / Alternative check:
Check by recomputing midpoint of A(2, -4) and B(8, 2):
((2 + 8)/2, (-4 + 2)/2) = (10/2, -2/2) = (5, -1), which matches P exactly. So the coordinates are correct.
Why Other Options Are Wrong:
• Any other option fails the midpoint check and would not average with A to give (5, -1).
Common Pitfalls:
• Forgetting to multiply by 2 before subtracting.
• Mixing up x and y while solving the two equations.
Final Answer:
(8, 2)
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