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Find the values of ‘a’ for which the vectors α = i + 2j + k, β = ai + j + 2k and γ = i + 2j + ak are coplanar. |
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Answer» Three vectors are coplanar if (if and only if) \(\vec a.(\vec b\times\vec c)=0\) Hence we have value of the matrix \(\begin{vmatrix}1 & 2 & 1 \\a & 1 & 2 \\1 & 2 & a\end{vmatrix}\) = 0 We have 2a2 - 3a + 1 = 0 2a2 - 2a - a + 1 = 0 Solving this quadratic equation we get a = 1, a = \(\cfrac12\) |
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