Exercise 4.1

Q1

1. The cost of a notebook is twice the cost of a pen. Write a linear equation in two variables to represent this statement. (Take the cost of a notebook to be Rs. x and that of a pen to be Rs. y).

Sol

Solution:

Let the cost of a notebook be = ₹ x

Let the cost of a pen be = ₹ y

Given: The cost of a notebook is twice the cost of a pen i.e Cost of a notebook = 2 × cost of a pen

= 212 ×

x = 2y ⇒ x - 2y = 0

Thus, x−2y=0 is the linear equation in two variables to represent the statement, ‘The cost of a notebook is twice the cost of a pen.

Q2

2. Express the following linear equations in the form ax + by + c = 0 and indicate the values of a, b and c in each case:

(i) 2x + 3y =

(ii) x – y5 – 10 = 0

(iii) –2x + 3y = 6

(iv) x = 3y

(v) 2x = –5y

(vi) 3x + 2 = 0

(vii) y – 2 = 0

(viii) 5 = 2x

Sol

(i) 2x + 3y =

The equation 2x + 3y = can be written as:

2x + 3y - = 0

Comparing we get: a = , b = and c = -9.355559.35