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The position vectors of the vertices A, B, C and D of a quadrilateral ABCD are given by \(3\hat{i} +4\hat{j}-2\hat{k}\), \(4\hat{i}-4\hat{j}-3\hat{k}\), \(2\hat{i} - 3\hat{j}+2\hat{k}\) and \(6\hat{i}-2\hat{j}+\hat{k}\) respectively. What is the angle between the diagonals AC and BD of the quadrilateral?

This question was previously asked in
NDA 2 2025 GAT Question Paper (14-Sep-2025)
The correct answer is

\(90^\circ\)

To find the angle between the diagonals AC and BD of the quadrilateral ABCD, we need to determine the vectors for AC and BD using the given position vectors of the vertices A, B, C, and D.

  1. First, let's determine the vector \(\overrightarrow{AC}\). Given:
    • Position vector of A: \(3\hat{i} +4\hat{j}-2\hat{k}\)
    • Position vector of C: \(2\hat{i} - 3\hat{j} + 2\hat{k}\)
  2. Now, let's determine the vector \(\overrightarrow{BD}\). Given:
    • Position vector of B: \(4\hat{i} - 4\hat{j} - 3\hat{k}\)
    • Position vector of D: \(6\hat{i} - 2\hat{j} + \hat{k}\)
  3. Next, we compute the dot product of vectors \(\overrightarrow{AC}\) and \(\overrightarrow{BD}\):
    • Dot product: \((-1)(2) + (-7)(2) + (4)(4) = -2 - 14 + 16 = 0\)
  4. The vectors are perpendicular if their dot product is zero. Therefore, the angle between \(\overrightarrow{AC}\) and \(\overrightarrow{BD}\) is \(90^\circ\).

Thus, the correct answer is \(90^\circ\).

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Similar Questions

  1. Let \(\vec{a}, \vec{b}, \vec{c}\) be three non-zero vectors such that   \(\vec{a}\times \vec{b} = \vec{c} \) . Consider the following statements:

    1.  \(\vec a\)  is unique if  \(\vec b\)  and  \(\vec c\)  are given

    2.  \(\vec c\)  is unique if  \(\vec a\)  and  \(\vec b\)  are given

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  2. In a right angled triangle ABC, if the hypotenuse AC = p, then what is \(\overrightarrow {{\rm{AB}}} \cdot \overrightarrow {{\rm{AC}}} + \overrightarrow {{\rm{BC}}} \cdot \overrightarrow {{\rm{BA}}} + \overrightarrow {{\rm{CA}}} \cdot \overrightarrow {{\rm{CB}}} \)  equal to?

  3. What is \({\rm{\vec c}}\) equal to?

  4. If \({\rm{\vec d}} = {\rm{x\hat i}} + {\rm{y\hat j}} + {\rm{z\hat k}}\) , then which of the following equations is/are correct?

    1. y – x = 4

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  5. What is \({\rm{\vec a}} \cdot {\rm{\vec b}} + {\rm{\vec b}} \cdot {\rm{\vec c}} + {\rm{\vec c}} \cdot {\rm{\vec a}}\) equal to?

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  7. What is the fourth vertex \(D\)?
  8. Let \(\vec{a} = \hat{i} - \hat{j} + \hat{k}\) and \(\vec{b} = \hat{i} + 2\hat{j} - \hat{k}\). If \(\vec{a} \times (\vec{b} \times \vec{a}) = \alpha\hat{i} - \beta\hat{j} + \gamma\hat{k}\), then what is the value of \(\alpha + \beta + \gamma\)?
  9. Let \(\vec{p}=\vec{a}-\vec{b}\), \(\vec{q}=\vec{a}+\vec{b}\). If \(|\vec{a}|=|\vec{b}|= 2\) and \(\vec{a}\cdot\vec{b} = 2\), then what is the value of \(|\vec{p}\times\vec{q}|\)?
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Important Questions from Vector Algebra

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  3. If non - zero a, b, c are such that a + b + c = 0, then the value of \(\frac{a^2}{bc} + \frac{b^2}{ac} + \frac{c^2}{ab}\) is

  4. Vector a = 3i + 2j – 6k, vector b = 4i – 3j + k, angle between above vectors is

  5. Two forces F1 and F2 are used to pull a car, which met an accident. The angle between the two force is θ. Find the value of θ for the resultant force is equal to \(\sqrt{(F_1^2 + F_2^2)}\)

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