The value of $k$ such that the lines $2 x-3 y+k=0, \quad 3 x-4 y-13=0 \quad$ and $8 x-11 y-33=0$ are…

The value of $k$ such that the lines $2 x-3 y+k=0, \quad 3 x-4 y-13=0 \quad$ and $8 x-11 y-33=0$ are concurrent, is
  1. $20$
  2. $-7$
  3. $7$
  4. $-20$

Solution

Since, the lines $ \begin{aligned} & 2 x-3 y+k=0,3 x-4 y-13=0 \\ & \text { and } \quad 8 x-11 y-33=0 \\ & \text { are concurrent } \\ & \therefore \quad\left|\begin{array}{ccc} 2 & -3 & k \\ 3 & -4 & -13 \\ 8 & -11 & -33 \end{array}\right|=0 \\ & \Rightarrow \quad 2(132-143)+3(-99+104) \\ & +k(-33+32)=0 \\ & \Rightarrow \quad-22+15-k=0 \\ & \Rightarrow \quad k=-7 \\ & \end{aligned} $

Asked in: AP EAMCET 2008

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