KCET · Maths · Linear Programming
The distance of the point \((1,2,-4)\) from the line \(\frac{x-3}{2}=\frac{y-3}{3}=\frac{z+5}{6}\) is
- A \(\frac{293}{7}\)
- B \(\frac{\sqrt{293}}{7}\)
- C \(\frac{293}{49}\)
- D \(\frac{\sqrt{293}}{49}\)
Answer & Solution
Correct Answer
(B) \(\frac{\sqrt{293}}{7}\)
Step-by-step Solution
Detailed explanation
Given, point \((1,2,-4)\).
\(\begin{aligned}
&\text { and line } \frac{x-3}{2}=\frac{y-3}{3}=\frac{z+5}{6}=\lambda \text { (let) } \\
&\begin{aligned}
& \therefore & x &=2 \lambda+3 \\
& \therefore & x &=2 \lambda+3, y=3 \lambda+3, z=6 \lambda-5
\end{aligned}
\end{aligned}\)
Let \(P(2 \lambda+3,3 \lambda+3,6 \lambda-5)\) be the foot of perpendicular from \(A(1,2,4)\)
\(\therefore\) Direction ratios of \(A P\) are
\(2 \lambda+3-1,3 \lambda+3-2,6 \lambda-5+4\)
i.e., \(2 \lambda+2,3 \lambda+1,6 \lambda-1\)
And direction ratios of given line are \(2,3,6\).
Since, \(\Lambda P \perp\) given line
\(\begin{array}{cc}\therefore & 2(2 \lambda+2)+3(3 \lambda+1)+6(6 \lambda-1)=0 \\ \Rightarrow & 4 \lambda+4+9 \lambda+3+36 \lambda-6=0\end{array}\)
\(\Rightarrow \quad 49 \lambda+1=0\)
\(\Rightarrow \quad \lambda=-\frac{1}{49}\)
\(\therefore P(2 \lambda+3,3 \lambda+3,6 \lambda-5)\)
\(\therefore\) Distance of the point \((1,2,-4)\) from the given line,
\(\begin{aligned}
A P^{2} &=(2 \lambda+2)^{2}+(3 \lambda+1)^{2}+(6 \lambda-1)^{2} \\
&=4 \lambda^{2}+4+8 \lambda+9 \lambda^{2}+1+6 \lambda+36 \lambda^{2}+1-12 \lambda \\
&=49 \lambda^{2}+6+2 \lambda \\
&=49\left(-\frac{1}{49}\right)^{2}+6+2\left(-\frac{1}{49}\right)
\end{aligned}\)
\(\begin{aligned} &=\frac{1}{49}+6-\frac{2}{49} \\ &=6-\frac{1}{49}=\frac{293}{49} \\ \Rightarrow A P &=\frac{\sqrt{293}}{7} \end{aligned}\)
\(\begin{aligned}
&\text { and line } \frac{x-3}{2}=\frac{y-3}{3}=\frac{z+5}{6}=\lambda \text { (let) } \\
&\begin{aligned}
& \therefore & x &=2 \lambda+3 \\
& \therefore & x &=2 \lambda+3, y=3 \lambda+3, z=6 \lambda-5
\end{aligned}
\end{aligned}\)
Let \(P(2 \lambda+3,3 \lambda+3,6 \lambda-5)\) be the foot of perpendicular from \(A(1,2,4)\)
\(\therefore\) Direction ratios of \(A P\) are
\(2 \lambda+3-1,3 \lambda+3-2,6 \lambda-5+4\)
i.e., \(2 \lambda+2,3 \lambda+1,6 \lambda-1\)
And direction ratios of given line are \(2,3,6\).
Since, \(\Lambda P \perp\) given line
\(\begin{array}{cc}\therefore & 2(2 \lambda+2)+3(3 \lambda+1)+6(6 \lambda-1)=0 \\ \Rightarrow & 4 \lambda+4+9 \lambda+3+36 \lambda-6=0\end{array}\)
\(\Rightarrow \quad 49 \lambda+1=0\)
\(\Rightarrow \quad \lambda=-\frac{1}{49}\)
\(\therefore P(2 \lambda+3,3 \lambda+3,6 \lambda-5)\)
\(\therefore\) Distance of the point \((1,2,-4)\) from the given line,
\(\begin{aligned}
A P^{2} &=(2 \lambda+2)^{2}+(3 \lambda+1)^{2}+(6 \lambda-1)^{2} \\
&=4 \lambda^{2}+4+8 \lambda+9 \lambda^{2}+1+6 \lambda+36 \lambda^{2}+1-12 \lambda \\
&=49 \lambda^{2}+6+2 \lambda \\
&=49\left(-\frac{1}{49}\right)^{2}+6+2\left(-\frac{1}{49}\right)
\end{aligned}\)
\(\begin{aligned} &=\frac{1}{49}+6-\frac{2}{49} \\ &=6-\frac{1}{49}=\frac{293}{49} \\ \Rightarrow A P &=\frac{\sqrt{293}}{7} \end{aligned}\)
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