Mathematics · 2021
JEE Main · 25 July 2021, Shift 1 · Q71
Let the vectors (2+ a + b ) i +( a +2 b + c ) j -( b + c ) k, (1+ b ) i +2 b j - b k and (2+ b ) i +2 b j +(1- b ) k, a, b, c ∈ R be co-planar. Then…
Let the vectors
$$\begin{aligned}
& (2+\mathrm{a}+\mathrm{b}) \hat{i}+(\mathrm{a}+2 \mathrm{~b}+\mathrm{c}) \hat{j}-(\mathrm{b}+\mathrm{c}) \hat{k}, \\
& (1+\mathrm{b}) \hat{i}+2 \mathrm{~b} \hat{j}-\mathrm{b} \hat{k} \text { and }(2+\mathrm{b}) \hat{i}+2 \mathrm{~b} \hat{j}+(1-\mathrm{b}) \hat{k}, \mathrm{a}, \mathrm{~b}, \mathrm{c} \in \mathbf{R}
\end{aligned}
$$
be co-planar. Then which of the following is true ?
Official answer
(1)
$\displaystyle 2 b=a+c$
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JEE Main 2021 Mathematics question, with the answer from NTA’s final answer key. Where our answers come from.