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Question #41878

Difficulty: 8/10 | 🟢 Free

The Question

Let w⃗1=2i^−3j^+k^\vec{w}_1 = 2\hat{i} - 3\hat{j} + \hat{k}, w⃗2=i^+2j^−2k^\vec{w}_2 = \hat{i} + 2\hat{j} - 2\hat{k}, and w⃗3=−2i^+j^+3k^\vec{w}_3 = -2\hat{i} + \hat{j} + 3\hat{k}. For j∈{1,2,3}j \in \{1, 2, 3\}, let e^j\hat{e}_j denote the standard basis vectors i^,j^,k^\hat{i}, \hat{j}, \hat{k} respectively. Let p⃗k,j\vec{p}_{k,j} be the vector projection of w⃗k\vec{w}_k onto e^j\hat{e}_j. Define the vectors u⃗j=∑k=13∣p⃗k,j∣w⃗k\vec{u}_j = \sum_{k=1}^3 |\vec{p}_{k,j}| \vec{w}_k for j=1,2,3j=1, 2, 3. If VV is the volume of the parallelepiped determined by u⃗1,u⃗2,u⃗3\vec{u}_1, \vec{u}_2, \vec{u}_3, find the value of VV.

Options

  • A.

    144

  • B.

    324

  • C.

    18

  • D.

    8

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Bridge

Practice problems that bridge the gap between foundational theory and advanced practical application.

Concepts Behind This Question

Sigma Notation Properties|Linear Independence vs Dependence|Dot Product Projection Sign

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to distinguish between a dot product and the magnitude of a vector projection in a summation basis.

The trap lies in assuming ∣p⃗k,j∣=w⃗k⋅e^j|\vec{p}_{k,j}| = \vec{w}_k \cdot \hat{e}_j, which ignores the absolute value sign inherent to vector magnitude.

If a student makes this error, the coefficient matrix CC becomes WTW^T, leading to the incorrect volume det⁡(WWT)=det⁡(W)2=324\det(W W^T) = \det(W)^2 = 324.

Recognizing that the projection magnitude forces all scalar coefficients to be strictly positive changes the linear transformation matrix, correctly yielding a volume of 144.

Quick Facts About This Question

Question Information

SubjectMathematics
ChapterSequences and Series - Class 11
ConceptSigma Notation Properties
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree