CBSE Class 9 Mathematics Question 7 of 9

Linear Equations in Two Variables — Question 1

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Question 1

Which one of the following options is true, and why?

y = 3x + 5 has

(i) a unique solution

(ii) only two solutions

(iii) infinitely many solutions

Answer

Given, linear equation y = 3x + 5

We know that,

y = 3x + 5 is a linear equation in two variables in the form of ax + by + c = 0

Substituting x = 0, in y = 3x + 5, we get :

⇒ y = 3(0) + 5 = 0 + 5 = 5.

∴ (0, 5) is one solution.

Substituting x = 1, in y = 3x + 5, we get :

⇒ y = 3(1) + 5 = 3 + 5 = 8.

∴ (1, 8) is another solution.

Substituting x = 2, in y = 3x + 5, we get :

⇒ y = 3(2) + 5 = 6 + 5 = 11.

∴ (2, 11) is another solution.

Clearly, for different values of x, we get different values of y.

Thus, y = 3x + 5 has infinitely many solutions.

Hence, Option (iii) is the correct answer.

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Linear Equations in Two Variables — Interactive Study Guide

Infinite Solutions

A linear equation in two variables has infinitely many solutions. Each solution is a point on the line. The line extends forever in both directions.

Key Concept: One equation, two unknowns = infinite solutions. You need TWO equations to get a unique solution (Class X topic).

Graphing Made Easy

  1. Rewrite as y = mx + c.
  2. Make a table: choose 3 values of x, calculate y for each.
  3. Plot the 3 points. If they’re collinear, draw the line.

Special Lines

y = 3: Horizontal line, 3 units above x-axis.

x = −2: Vertical line, 2 units left of y-axis.

y = x: Line at 45° through origin.

Quick Self-Check

  1. Is (2, 3) a solution of x + y = 5? (Yes: 2 + 3 = 5)
  2. Give 3 solutions of y = 2x. ((0,0), (1,2), (2,4))
  3. What is the equation of the x-axis? (y = 0)

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