Let $\lambda_{1}, \lambda_{2}$ be the values of $\lambda$ for which the points $\left(\frac{5}{2}, 1, \lambda\right)$ and $(-2,0,1)$ are at equal distance from the plane $2 x+3 y-6 z+7=0$. If $\lambda_{1} > \lambda_{2}$, then the distance of the point $\left(\lambda_{1}-\lambda_{2}, \lambda_{2}, \lambda_{1}\right)$ from the line $\frac{x-5}{1}=\frac{y-1}{2}=\frac{z+7}{2}$ is ____________.
Solution
Since $\left(\frac{5}{2}, 1, \lambda\right)$ and $(-2,0,1)$ are equidistant
<br/><br/>from plane $2 x+3 y-6 z+7=0$
<br/><br/>$$
\begin{aligned}
& \therefore\left|\frac{2\left(\frac{5}{2}\right)+3(1)-6(\lambda)+7}{\sqrt{2^2+3^2+6^2}}\right|=\left|\frac{2(-2)+3(0)-6(1)+7}{\sqrt{2^2+3^2+6^2}}\right| \\\\
& \Rightarrow|5+3-6 \lambda+7|=|-4-6+7| \\\\
& \Rightarrow|15-6 \lambda|=|-3| \\\\
& \Rightarrow 15-6 \lambda= \pm 3 \\\\
& \Rightarrow 15-6 \lambda=3 \text { or } 15-6 \lambda=-3 \\\\
& \Rightarrow 6 \lambda=12 \text { or } 6 \lambda=18 \\\\
& \Rightarrow \lambda=2 \text { or } \lambda=3
\end{aligned}
$$
<br/><br/>$$
\begin{aligned}
& \because \lambda_1>\lambda_2 \\\\
& \therefore \lambda_1=3 \text { and } \lambda_2=2
\end{aligned}
$$
<br/><br/>So, point will be $(1,2,3)$
<br/><br/>Let $\mathrm{M}_0=(1,2,3)$
<br/><br/>$M_1$ is the point through which line passes i.e, $(5,1,-7)$
<br/><br/>and $\vec{s}=\hat{i}+2 \hat{j}+2 \hat{k}$
<br/><br/>$$
\therefore \overrightarrow{\mathrm{M}_0 \mathrm{M}_1}=4 \hat{i}-\hat{j}-10 \hat{k}
$$
<br/><br/>Now, required distance $=\left|\frac{\overrightarrow{\mathrm{M}_0 \mathrm{M}_1} \times \vec{s}}{|\vec{s}|}\right|$
<br/><br/>$$
\begin{aligned}
& =\frac{|(4 \hat{i}-\hat{j}-10 \hat{k}) \times(\hat{i}+2 \hat{j}+2 \hat{k})|}{\sqrt{1+4+4}} \\\\
& =\frac{|18 \hat{i}-18 \hat{j}+9 \hat{k}|}{3}=9
\end{aligned}
$$
About this question
Subject: Mathematics · Chapter: Three Dimensional Geometry · Topic: Direction Cosines and Ratios
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