What is the value of x for which the points A (-1, 3), B (2, x) and C (5, -1) are collinear?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 1
For three points to be collinear, the slopes between any two pairs must be equal.
Given points:
- $A(-1, 3)$
- $B(2, x)$
- $C(5, -1)$
Step 1: Slope of AC
$m_{AC} = \frac{-1 - 3}{5 - (-1)} = \frac{-4}{6} = -\frac{2}{3}$
Step 2: Slope of AB
$m_{AB} = \frac{x - 3}{2 - (-1)} = \frac{x - 3}{3}$
Step 3: Set slopes equal
$\frac{x - 3}{3} = -\frac{2}{3}$
$x−3=−2$
$x=1$
Correct answer: 1