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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Vector Algebra

NDA 2025 · Mathematics · Vector Algebra

What is the area of the parallelogram whose sides are represented...

What is the area of the parallelogram whose sides are represented by the vectors i^+2j^+3k^\hat{i} + 2\hat{j} + 3\hat{k} and 2i^+j^+2k^2\hat{i} + \hat{j} + 2\hat{k}?

Options

  1. A1226\dfrac{1}{2}\sqrt{26} square units
  2. B1227\dfrac{1}{2}\sqrt{27} square units
  3. C26\sqrt{26} square units
  4. D27\sqrt{27} square units

Correct answer

C. 26\sqrt{26} square units

Step-by-step solution

Let a⃗=i^+2j^+3k^\vec{a} = \hat{i} + 2\hat{j} + 3\hat{k} and b⃗=2i^+j^+2k^\vec{b} = 2\hat{i} + \hat{j} + 2\hat{k}.

The area of the parallelogram with adjacent sides a⃗\vec{a} and b⃗\vec{b} is given by ∣a⃗×b⃗∣|\vec{a} \times \vec{b}|.

a⃗×b⃗=∣i^ and j^ and k^1 and 2 and 32 and 1 and 2∣\vec{a} \times \vec{b} = \begin{vmatrix} \hat{i} \text{ and } \hat{j} \text{ and } \hat{k} \\ 1 \text{ and } 2 \text{ and } 3 \\ 2 \text{ and } 1 \text{ and } 2 \end{vmatrix}

=i^(4−3)−j^(2−6)+k^(1−4)= \hat{i}(4 - 3) - \hat{j}(2 - 6) + \hat{k}(1 - 4)

=i^+4j^−3k^= \hat{i} + 4\hat{j} - 3\hat{k}

The magnitude of the cross product is:

∣a⃗×b⃗∣=12+42+(−3)2|\vec{a} \times \vec{b}| = \sqrt{1^2 + 4^2 + (-3)^2}

=1+16+9=26= \sqrt{1 + 16 + 9} = \sqrt{26}

The area of the parallelogram is 26squareunits.<br><br>Answer:26\sqrt{26} square units.<br><br>Answer: \sqrt{26} square units
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