Question

Find the value of $x$ for the points $(x,-1)(2,1)(4,5)$ are collinear.

Answer 1

$SlopeAB=slopeBC$

$-\left(\frac{1-(-1)}{2-x}\right)=-\left(\frac{5-\left(1\right)}{4-2}\right)$

$\Rightarrow \frac{2}{2-x}=\frac{4}{2}\Rightarrow 1=2-x$

$\Rightarrow x=1$