Medium INTEGER +4 / -1 PYQ · JEE Mains 2023

Let $\overrightarrow a$, $\overrightarrow b$ and $\overrightarrow c$ be three non-zero non-coplanar vectors. Let the position vectors of four points $A,B,C$ and $D$ be $$\overrightarrow a - \overrightarrow b + \overrightarrow c ,\lambda \overrightarrow a - 3\overrightarrow b + 4\overrightarrow c , - \overrightarrow a + 2\overrightarrow b - 3\overrightarrow c $$ and $2\overrightarrow a - 4\overrightarrow b + 6\overrightarrow c$ respectively. If $\overrightarrow {AB} ,\overrightarrow {AC}$ and $\overrightarrow {AD}$ are coplanar, then $\lambda$ is equal to __________.

Answer (integer) 2

Solution

$\overline{A B}=(\lambda-1) \bar{a}-2 \bar{b}+3 \bar{c}$ <br/><br/> $\overline{A C}=2 \bar{a}+3 \bar{b}-4 \bar{c}$<br/><br/>$\overline{A D}=\bar{a}-3 \bar{b}+5 \bar{c}$<br/><br/>$$ \left|\begin{array}{ccc} \lambda-1 & -2 & 3 \\ -2 & 3 & -4 \\ 1 & -3 & 5 \end{array}\right|=0 $$<br/><br/>$\Rightarrow(\lambda-1)(15-12)+2(-10+4)+3(6-3)=0$<br/><br/>$\Rightarrow(\lambda-1)=1 \Rightarrow \lambda=2$

About this question

Subject: Mathematics · Chapter: Vector Algebra · Topic: Types of Vectors

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