MCQ
If points $(5, 5)$, $(10, k)$ and $(-5, 1)$ are collinear, then $k =$
  • A
    $3$
  • B
    $5$
  • $7$
  • D
    $9$

Answer

Correct option: C.
$7$
c
(c) According to the condition $\left| {\,\begin{array}{*{20}{c}}5&5&1\\{10}&k&1\\{ - 5}&1&1\end{array}\,} \right| = 0$

$ \Rightarrow \,\,$$\left| {\,\begin{array}{*{20}{c}}5&5&1\\5&{k - 5}&0\\{ - 10}&{1 - 5}&0\end{array}\,} \right| = 0\,\, $

$\Rightarrow \,\,k = 7$.

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