Difficulty: Medium
Correct Answer: 12.5
Explanation:
Introduction / Context:
This problem tests coordinate geometry basics: computing slope from two points and solving for an unknown coordinate. The slope formula is m = (y2 - y1)/(x2 - x1). Here, one x-coordinate is unknown, and we use the given slope to form an equation and solve it.
Given Data / Assumptions:
Concept / Approach:
Substitute coordinates into the slope formula. Then solve the resulting fraction equation by cross-multiplication. Carefully keep the order of subtraction consistent because changing point order changes the sign of both numerator and denominator, but the slope must remain the given value.
Step-by-Step Solution:
Slope between A(x, -3) and B(5, 2): m = (2 - (-3)) / (5 - x)
Compute numerator: 2 - (-3) = 5
So m = 5 / (5 - x)
Given m = -2/3, set 5 / (5 - x) = -2/3
Cross-multiply: 5*3 = -2*(5 - x)
15 = -10 + 2x
Add 10 to both sides: 25 = 2x
So x = 25/2 = 12.5
Verification / Alternative check:
Plug x = 12.5 back: denominator 5 - 12.5 = -7.5, so slope = 5/(-7.5) = -2/3, correct. This confirms the solution.
Why Other Options Are Wrong:
10 and 4 typically come from using (x - 5) instead of (5 - x) without adjusting signs properly.
-4 and -14 come from sign errors when distributing -2 across (5 - x).
Common Pitfalls:
Forgetting that 5 - x can be negative, mishandling negative signs during cross-multiplication, or incorrectly computing 2 - (-3). Another common mistake is swapping the denominator to x - 5 but not changing the sign of the slope.
Final Answer:
x = 12.5
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