1983

JEE Main 1983 Mathematics question on Vector Algebra

The volume of the parallelopiped whose sides are given by OA⃗=2i^−3j^\vec{OA} = 2\hat{i} - 3\hat{j}, OB⃗=i^+j^−k^\vec{OB} = \hat{i} + \hat{j} - \hat{k}, OC⃗=3i^−k^\vec{OC} = 3\hat{i} - \hat{k}, is
  1. A.
    413\frac{4}{13}
  2. B.
    44
  3. C.
    27\frac{2}{7}
  4. D.
    None of these
Show answer and solution

Correct option: B

Solution

The volume equals |[OA, OB, OC]|, the absolute value of the scalar triple product.

Scalar triple product = OA · (OB × OC)

Compute as the determinant:
|2 -3 0|
|1 1 -1|
|3 0 -1|

= 2[(1)(−1) − (−1)(0)] − (−3)[(1)(−1) − (−1)(3)] + 0
= 2[−1 − 0] + 3[−1 + 3]
= 2(−1) + 3(2)
= −2 + 6 = 4

Volume = |4| = 4.

[1983]

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