If the points with position vectors $$\alpha \hat{i}+10 \hat{j}+13 \hat{k}, 6 \hat{i}+11 \hat{j}+11 \hat{k}, \frac{9}{2} \hat{i}+\beta \hat{j}-8 \hat{k}$$ are collinear, then $(19 \alpha-6 \beta)^{2}$ is equal to :
Solution
Given : Points with position vectors
<br/><br/>$\alpha \hat{i}+10 \hat{j}+13 \hat{k}, 6 \hat{i}+11 \hat{j}+11 \hat{k}$
<br/><br/>and $\frac{9}{2} \hat{i}+\beta \hat{j}-8 \hat{k}$ are collinear.
<br/><br/>So, $\frac{\alpha-6}{6-\frac{9}{2}}=\frac{10-11}{11-\beta}=\frac{13-11}{11+8}$
<br/><br/>$$
\begin{aligned}
& \Rightarrow \frac{2(\alpha-6)}{3}=\frac{-1}{11-\beta}=\frac{2}{19} \\\\
& \Rightarrow \frac{2}{3}(\alpha-6)=\frac{2}{19}
\end{aligned}
$$
<br/><br/>$$
\begin{aligned}
& \Rightarrow 19 \alpha-114=3 \Rightarrow 19 \alpha=117 \\\\
& \Rightarrow \alpha=\frac{117}{19}
\end{aligned}
$$
<br/><br/>And, $\frac{-1}{11-\beta}=\frac{2}{19}$
<br/><br/>$$
\begin{aligned}
& \Rightarrow-19=22-2 \beta \\\\
& \Rightarrow 2 \beta=41 \\\\
& \Rightarrow \beta=\frac{41}{2}
\end{aligned}
$$
<br/><br/>$$
\begin{aligned}
& \therefore(19 \alpha-6 \beta)^2=\left(19 \times \frac{117}{19}-\frac{6 \times 41}{2}\right)^2 \\\\
& =(117-123)^2=36
\end{aligned}
$$
About this question
Subject: Mathematics · Chapter: Vector Algebra · Topic: Types of Vectors
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