Answer:
k = 11
Step-by-step explanation:
Given the points are collinear then the slopes between consecutive points are equal.
Using the slope formula
m = [tex]\frac{y_{2}-y_{1} }{x_{2}-x_{1} }[/tex]
with (x₁, y₁ ) = (5, 1) and (x₂, y₂ ) = (1, - 1)
m = [tex]\frac{-1-1}{1-5}[/tex] = [tex]\frac{-2}{-4}[/tex] = [tex]\frac{1}{2}[/tex]
Repeat with another 2 points and equate to [tex]\frac{1}{2}[/tex]
with (x₁, y₁ ) = (1, - 1) and (x₂, y₂ ) = (k, 4)
m = [tex]\frac{4+1}{k-1}[/tex] , then
[tex]\frac{5}{k-1}[/tex] = [tex]\frac{1}{2}[/tex] ( cross- multiply )
k - 1 = 10 ( add 1 to both sides )
k = 11
