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JEE Advanced · Mathematics · 19. Determinants

Consider the lines given by
\[
L_1: x+3 y-5=0, L_2: 3 x-k y-1=0, L_3: 5 x+2 y-12=0
\]
Match the Statements/Expressions in Column I with the Statements/Expressions in Column II.

  1. A
    (A) r, (B) p,s, (C) s, (D) p,s
  2. B
    (A) s, (B) p,q,r, (C) r, (D) p,q
  3. C
    (A) s, (B) p,q, (C) r, (D) p,q,s
  4. D
    (A) r, (B) p,q, (C) s, (D) p,q
Verified Solution

Answer & Solution

Correct Answer

(C)
(A) s, (B) p,q, (C) r, (D) p,q,s

Step-by-step Solution

Detailed explanation

(A) Solving equations \(L_1\) and \(L_3\),
\[
\begin{aligned}
\frac{x}{-36+10} & =\frac{y}{+12-25}=\frac{1}{2-15} \\
x & =2, y=1
\end{aligned}
\]
\(L_1, L_2, L_3\) are concurrent, if point \((2,1)\) lies on \(L_2\).
\[
\therefore \quad 6-k-1=0 \Rightarrow k=5
\]
(B) Either \(L_1\) is parallel to \(L_2\), or \(L_3\) is parallel to \(L_2\), then
\[
\begin{aligned}
& \frac{1}{3}=\frac{3}{-k} \text { or } \frac{3}{5}=\frac{-k}{2} \\
& k=-9 \quad \text { or } \quad k=-\frac{6}{5}
\end{aligned}
\]
\[
\Rightarrow \quad k=-9 \text { or } k=-\frac{6}{5}
\]
(C) \(L_1, L_2, L_3\) form a triangle, if they are not concurrent, or not parallel.
\[
\therefore \quad k \neq 5,-9,-\frac{6}{5} \Rightarrow k=\frac{5}{6}
\]
(D) \(L_1, L_2, L_3\) do not form a triangle, if
\[
k=5,-9,-\frac{6}{5}
\]
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