Search any question & find its solution
Question:
Answered & Verified by Expert
If the line $4 x+3 y-k=0,2 x+y+3=0$ and $3 x+2 y+k=0$ are concurrent, then the perpendicular distance from the point of concurrency of these lines to the line $3 x+4 y+2=0$ is
Options:
Solution:
1657 Upvotes
Verified Answer
The correct answer is:
3
$$
\begin{aligned}
& \text { (d) }\left|\begin{array}{ccc}
4 & 3 & -k \\
2 & 1 & 3 \\
3 & 2 & k
\end{array}\right|=0 \\
& \Rightarrow \quad 4(k-6)-3(2 k-9)-k(4-3)=0 \\
& \Rightarrow \quad 4 k-24-6 k+27-4 k+3 k=0 \Rightarrow 3 k=3 \\
& \Rightarrow \quad k=1 \\
& \therefore \quad L_1: 4 x+3 y-1=0 \\
& \quad L_2: 2 x+y+3=0
\end{aligned}
$$
Eqn. (1) - (Eqn. (2) $\times 2$ ),
$$
\begin{aligned}
& y=7 \\
\therefore \quad x & =-5
\end{aligned}
$$
$\therefore \quad$ Point of concurrency is $(-5,7)$
Distance from $(-5,7)$ to $3 x+4 y+2=0$
$$
\begin{aligned}
& \quad d=\left|\frac{3(-5)+4(7)+2}{\sqrt{3^2+4^2}}\right| \\
& \therefore \quad d=3 .
\end{aligned}
$$
\begin{aligned}
& \text { (d) }\left|\begin{array}{ccc}
4 & 3 & -k \\
2 & 1 & 3 \\
3 & 2 & k
\end{array}\right|=0 \\
& \Rightarrow \quad 4(k-6)-3(2 k-9)-k(4-3)=0 \\
& \Rightarrow \quad 4 k-24-6 k+27-4 k+3 k=0 \Rightarrow 3 k=3 \\
& \Rightarrow \quad k=1 \\
& \therefore \quad L_1: 4 x+3 y-1=0 \\
& \quad L_2: 2 x+y+3=0
\end{aligned}
$$
Eqn. (1) - (Eqn. (2) $\times 2$ ),
$$
\begin{aligned}
& y=7 \\
\therefore \quad x & =-5
\end{aligned}
$$
$\therefore \quad$ Point of concurrency is $(-5,7)$
Distance from $(-5,7)$ to $3 x+4 y+2=0$
$$
\begin{aligned}
& \quad d=\left|\frac{3(-5)+4(7)+2}{\sqrt{3^2+4^2}}\right| \\
& \therefore \quad d=3 .
\end{aligned}
$$
Looking for more such questions to practice?
Download the MARKS App - The ultimate prep app for IIT JEE & NEET with chapter-wise PYQs, revision notes, formula sheets, custom tests & much more.