If the points $2a+3b-c, a-2b+3c, 3a+\lambda b-2c$ and $a-6b+6c$ are coplanar, then the direction cosines of the vector $\lambda \hat{i}-2\lambda \hat{j}+\hat{k}$ are

  • A
    $\frac{2}{\sqrt{21}}, \frac{-4}{\sqrt{21}}, \frac{1}{\sqrt{21}}$
  • B
    $-\frac{2}{\sqrt{78}}, \frac{5}{\sqrt{78}}, \frac{7}{\sqrt{78}}$
  • C
    $\frac{4}{9}, \frac{-8}{9}, \frac{1}{9}$
  • D
    $\frac{2}{3}, -\frac{2}{3}, -\frac{1}{3}$

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