Question 30 of 70intermediate🔧 ApplyLong Answer4 marks

By using the concept of equation of a line, prove that the three points (3,0),(−2,−2)(3, 0), (-2, -2) and (8,2)(8, 2) are collinear.

Correct Answer

Let the three given points be A(3, 0), B(-2, -2) and C(8, 2).

Finding the equation of line through A and B:

Using the equation of line passing through two points (x1,y1)(x_1, y_1) and (x2,y2)(x_2, y_2):

y−y1=y2−y1x2−x1(x−x1)y - y_1 = \frac{y_2 - y_1}{x_2 - x_1}(x - x_1)

Substituting A(3, 0) and B(-2, -2):

y−0=−2−0−2−3(x−3)y - 0 = \frac{-2 - 0}{-2 - 3}(x - 3) y=−2−5(x−3)y = \frac{-2}{-5}(x - 3) y=25(x−3)y = \frac{2}{5}(x - 3)

Checking if point C lies on this line:

Substituting x=8x = 8 in the equation:

y=25(8−3)=25×5=2y = \frac{2}{5}(8 - 3) = \frac{2}{5} \times 5 = 2

Since the yy-coordinate of point C is 2, and substituting x=8x = 8 gives y=2y = 2, point C satisfies the equation of line AB.

Conclusion:

The point (x,y)(x, y) lies on the line with slope mm and through the fixed point (x0,y0)(x_0, y_0), if and only if its coordinates satisfy the equation. Since point C(8, 2) satisfies the equation of line passing through A and B, all three points lie on the same line. Hence, the three points (3,0),(−2,−2)(3, 0), (-2, -2) and (8,2)(8, 2) are collinear.

Exercise: EXERCISE 9.2 | Q: 19 | (Page 14)
For More Understanding

Explanation

This question tests the student's understanding of the equation of a line passing through two points and the concept of collinearity. The textbook context provides the formula for the equation of a line through two points, and the condition that three points are collinear if they lie on the same line.

The solution demonstrates finding the equation of line through two points and verifying if the third point satisfies that equation.

Solution Steps

  1. Step 1: Identify the three points as A(3, 0), B(-2, -2) and C(8, 2).

  2. Step 2: Find the equation of line passing through A(3, 0) and B(-2, -2) using the formula:

    y−y1=y2−y1x2−x1(x−x1)y - y_1 = \frac{y_2 - y_1}{x_2 - x_1}(x - x_1)
  3. Step 3: Simplify to get:

    y=25(x−3)y = \frac{2}{5}(x - 3)
  4. Step 4: Substitute x=8x = 8 in the equation to verify if point C lies on the line.

  5. Step 5: Since y=2y = 2 when x=8x = 8, and point C has coordinates (8,2)(8, 2), point C satisfies the equation of line AB.

  6. Step 6: Conclude that all three points lie on the same line and are collinear.