Aspire Faculty ID #18365 · Topic: AMU MCA 2016 · Just now
AMU MCA 2016

The value of $\lambda$ so that the vectors $a = 2\hat{i} - \hat{j} + \hat{k}$, $b = \hat{i} + 2\hat{j} - 3\hat{k}$ and $c = 3\hat{i} + \lambda \hat{j} + 5\hat{k}$ are coplanar is

Solution

Coplanar ⇒ scalar triple product = 0 $\left|\matrix{2 & -1 & 1 \cr 1 & 2 & -3 \cr 3 & \lambda & 5}\right| = 0$ Expand: $= 2(10+3\lambda) + 1(5+9) + 1(\lambda-6)$ $= 20 + 6\lambda + 14 + \lambda - 6$ $= 28 + 7\lambda = 0$ $\lambda = -4$

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