JAMB 2022 Mathematics · Question 23

The coordinates of the mid-point of the line joining the points (-3,5) and (2,10) is given by?

Options

  1. A.( 12\frac{1}{2}, 152\frac{15}{2} )
  2. B.( 12\frac{1}{2}, −152\frac{-15}{2} )
  3. C.( −12\frac{-1}{2}, −152\frac{-15}{2} )
  4. D.( −12\frac{-1}{2}, 152\frac{15}{2} )

Answer: D. ( −12\frac{-1}{2}, 152\frac{15}{2} )

Explanation written with AI and checked against the answer key

Analysis

To find the midpoint of a line segment joining two points (x1,y1)(x_1, y_1) and (x2,y2)(x_2, y_2), we use the midpoint formula. This formula calculates the average of the x-coordinates and the average of the y-coordinates.

Concept

The midpoint MM of a line segment with endpoints (x1,y1)(x_1, y_1) and (x2,y2)(x_2, y_2) is given by:

M=(x1+x22,y1+y22)M = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)
Step-by-Step Solution
  1. Identify the coordinates: • Point 1: (x1,y1)=(−3,5)(x_1, y_1) = (-3, 5) • Point 2: (x2,y2)=(2,10)(x_2, y_2) = (2, 10)
  1. Apply the midpoint formula for the x-coordinate: $xm=x1+x22=−3+22=−12x_m = \frac{x_1 + x_2}{2} = \frac{-3 + 2}{2} = \frac{-1}{2}$
  1. Apply the midpoint formula for the y-coordinate: $ym=y1+y22=5+102=152y_m = \frac{y_1 + y_2}{2} = \frac{5 + 10}{2} = \frac{15}{2}$
  1. Combine the coordinates: The midpoint is (−12,152)\left( \frac{-1}{2}, \frac{15}{2} \right).
Conclusion

Comparing our result to the given options, we find that it matches option D.

Exam Tip: When dealing with negative numbers in coordinate geometry, always be careful with the signs during addition. A common mistake is to subtract the numbers instead of adding them algebraically (e.g., −3+2-3 + 2 is −1-1, not −5-5). Always write out the signs clearly before calculating!

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