ICSE Class 10 • 2023 • 4 Marks

Coordinate Geometry: Perpendicular Bisector Equation

Official examination question with verified M1/A1 mark scheme and step-by-step mathematical reasoning.

Problem Statement

Find the equation of the perpendicular bisector of the line segment joining the points $A(4, 2)$ and $B(-2, 6)$.

Verified Solution & Marking Scheme

Find Midpoint M of AB
$M = \left(\frac{4 + (-2)}{2}, \frac{2 + 6}{2}\right) = \left(\frac{2}{2}, \frac{8}{2}\right) = (1, 4)$
Find Slope of AB and Perpendicular Slope
$m_{AB} = \frac{6 - 2}{-2 - 4} = \frac{4}{-6} = -\frac{2}{3}$ Since the perpendicular bisector is perpendicular to $AB$: $m_\perp = -\frac{1}{m_{AB}} = -\frac{1}{-2/3} = \frac{3}{2}$
Write Equation of Line Through M(1, 4)
$y - 4 = \frac{3}{2}(x - 1) \implies 2(y - 4) = 3(x - 1)$ $2y - 8 = 3x - 3 \implies 3x - 2y + 5 = 0$
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