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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Three Dimensional Geometry

NDA 2025 · Mathematics · Three Dimensional Geometry

A(1, 2, -1) , B(2, 5, -2) and C(4, 4, -3) are three vertices of a...

A(1,2,−1)A(1, 2, -1), B(2,5,−2)B(2, 5, -2) and C(4,4,−3)C(4, 4, -3) are three vertices of a rectangle. What is the area of the rectangle?

Options

  1. A88 square units
  2. B99 square units
  3. C66\sqrt{66} square units
  4. D68\sqrt{68} square units

Correct answer

C. 66\sqrt{66} square units

Step-by-step solution

The given vertices of the rectangle are A(1,2,−1)A(1, 2, -1), B(2,5,−2)B(2, 5, -2) and C(4,4,−3)C(4, 4, -3).

The direction ratios of the side ABAB are (2−1,5−2,−2−(−1))=(1,3,−1)(2-1, 5-2, -2-(-1)) = (1, 3, -1).
The length of the side ABAB is 12+32+(−1)2=1+9+1=11.<br><br>Thedirectionratiosoftheside\sqrt{1^2 + 3^2 + (-1)^2} = \sqrt{1 + 9 + 1} = \sqrt{11}.<br><br>The direction ratios of the sideBCareare(4-2, 4-5, -3-(-2)) = (2, -1, -1).<br>Thelengthoftheside.<br>The length of the sideBCis22+(−1)2+(−1)2=4+1+1=6is \sqrt{2^2 + (-1)^2 + (-1)^2} = \sqrt{4 + 1 + 1} = \sqrt{6}.

Now, checking the dot product of vectors AB→\overrightarrow{AB} and BC→\overrightarrow{BC}:
AB→⋅BC→=(1)(2)+(3)(−1)+(−1)(−1)=2−3+1=0\overrightarrow{AB} \cdot \overrightarrow{BC} = (1)(2) + (3)(-1) + (-1)(-1) = 2 - 3 + 1 = 0

Since the dot product is zero, ABAB is perpendicular to BCBC, which means AA, BB, and CC are consecutive vertices forming a right angle at BB.

The area of the rectangle is the product of its adjacent sides:
Area=AB×BC=11×6=66 square units\text{Area} = AB \times BC = \sqrt{11} \times \sqrt{6} = \sqrt{66} \text{ square units}

Answer: 66squareunits\sqrt{66} square units
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