Question:

If \(W\) is a subspace of \(V^3\), where \[ W=\{(a,b,c)\mid a+b+c=0\}, \] then \(\dim W=\)

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One independent linear equation in \(V^3\) reduces the dimension from \(3\) to \(2\).
  • \(2\)
  • \(3\)
  • \(1\)
  • \(0\)
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The Correct Option is A

Solution and Explanation

Concept:
The dimension of a subspace is the number of free parameters needed to describe its vectors. Given, \[ W=\{(a,b,c):a+b+c=0\} \] This is a subspace of \(V^3\).

Step 1: Use the condition.
\[ a+b+c=0 \] So, \[ c=-a-b \]

Step 2: Write general vector of \(W\).
\[ (a,b,c)=(a,b,-a-b) \] \[ (a,b,-a-b)=a(1,0,-1)+b(0,1,-1) \]

Step 3: Count independent parameters.
The vector depends on two arbitrary parameters: \[ a,\quad b \] Therefore, \[ \dim W=2 \]

Step 4: Final answer.
\[ \boxed{2} \]
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