Question:medium

Let ABCD be a parallelogram such that the coordinates of its three vertices A, B, C are (1, 1), (3, 4), and (−2, 8), respectively. Then, the coordinates of the vertex D are

Updated On: Jan 15, 2026
  • (−4, 5)

  • (4, 5) 

  • (−3, 4)

  • (0, 11) 

Show Solution

The Correct Option is A

Solution and Explanation

Given

Parallelogram ABCD with vertices:

  • \( A = (1, 1) \)
  • \( B = (3, 4) \)
  • \( C = (-2, 8) \)
  • \( D = (x, y) \) — unknown

The diagonals of a parallelogram bisect each other.

Step 1: Midpoint of Diagonal AC

Calculate the midpoint of diagonal AC: \[ \text{Midpoint}_{AC} = \left( \frac{1 + (-2)}{2}, \frac{1 + 8}{2} \right) = \left( \frac{-1}{2}, \frac{9}{2} \right) \]

Step 2: Coordinates of Point D

The midpoint of diagonal BD is: \[ \text{Midpoint}_{BD} = \left( \frac{3 + x}{2}, \frac{4 + y}{2} \right) \] As the diagonals bisect each other, their midpoints are identical: \[ \frac{3 + x}{2} = \frac{-1}{2} \quad \text{and} \quad \frac{4 + y}{2} = \frac{9}{2} \]

Step 3: Solve for x and y

Solve the equation for x: \[ \frac{3 + x}{2} = \frac{-1}{2} \Rightarrow 3 + x = -1 \Rightarrow x = -4 \]

Solve the equation for y: \[ \frac{4 + y}{2} = \frac{9}{2} \Rightarrow 4 + y = 9 \Rightarrow y = 5 \]

 Final Answer

The coordinates of point \( D \) are: \[ \boxed{(-4, 5)} \]

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