Given:
The three points are W(0,-2), I(2,0) and L(5,k).
To find:
The value of k for which the given points are collinear.
Solution:
We know that, three points are collinear if the area of the triangle formed by these three points is 0.
[tex]\dfrac{1}{2}|x_1(y_2-y_3)+x_2(y_3-y_1)+x_3(y_1-y_2)|=0[/tex]
[tex]x_1(y_2-y_3)+x_2(y_3-y_1)+x_3(y_1-y_2)=0[/tex]
The three points are W(0,-2), I(2,0) and L(5,k). So,
[tex]0(0-k)+2(k-(-2))+5(-2-0)=0[/tex]
[tex]0+2(k+2)+5(-2)=0[/tex]
[tex]2k+4-10=0[/tex]
[tex]2k-6=0[/tex]
Adding 6 on both sides, we get
[tex]2k=6[/tex]
[tex]k=\dfrac{6}{2}[/tex]
[tex]k=3[/tex]
Therefore, the correct option is E.