Question: Find the value of k for which the points $ A(-1,3), $ $ B(2,k) $ and $ C(5,-1) $ are collinear
Options:
A) 1
B) 3
C) 2
D) 4
Show Answer
Answer:
Correct Answer: A
Solution:
- Here, $ x _1=-1, $ $ x _2=2, $ $ x _3=5, $ $ y _1=3, $ $ y _2=k $ and $ y _3=-1 $
Since, points are collinear,
Then, area $ (\Delta )=0 $
$ \Rightarrow $ $ x _1(y _2-y _3)+x _2(y _3-y _1)+x _3(y _1-y _2)=0 $
$ \Rightarrow $ $ -1(k+1)+2(-1-3)+5(3-k)=0 $
$ \Rightarrow $ $ -k-1-8+15-5k=0 $
$ \Rightarrow $ $ 6k=6 $
$ \Rightarrow $ $ k=1 $