Class 7 Maths Chapter 4 Exercise 4.2 Pdf Notes NCERT Solutions

Class 7 Maths Chapter 4 Simple Equations Exercise 4.2 pdf notes:-

Exercise 4.2 Class 7 maths Chapter 4 Pdf Notes:-

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REVIEW OF WHAT WE KNOW
Note, (4.1) and (4.2) are equations. Let us recall what we learnt about equations in
Class VI. An equation is a condition on a variable. In equation (4.1), the variable is x;
in equation (4.2), the variable is y.
The word variable means something that can vary, i.e. change. A variable takes on
different numerical values; its value is not fixed. Variables are denoted usually by
letters of the alphabets, such as x, y, z, l, m, n, p, etc. From variables, we form
expressions. The expressions are formed by performing operations like addition, subtraction,
multiplication and division on the variables. From x, we formed the expression (4x + 5).
For this, first we multiplied x by 4 and then added 5 to the product. Similarly, from y, we
formed the expression (10y – 20). For this, we multiplied y by 10 and then subtracted 20
from the product. All these are examples of expressions.
The value of an expression thus formed depends upon the chosen value of the variable.
As we have already seen, when x = 1, 4x + 5 = 9; when x = 5, 4x + 5 = 25. Similarly,
when x = 15, 4 x + 5 = 4×15 + 5 = 65;
when x = 0, 4 x + 5 = 4 × 0 + 5 = 5; and so on.
Equation (4.1) is a condition on the variable x. It states that the value of the expression
(4x + 5) is 65. The condition is satisfied when x = 15. It is the solution to the equation
4x + 5 = 65. When x = 5, 4x + 5 = 25 and not 65. Thus x = 5 is not a solution to the
equation. Similarly, x = 0 is not a solution to the equation. No value of x other than 15
satisfies the condition 4x + 5 = 65.

The value of the expression (10y – 20) depends on the value of y. Verify this by
giving five different values to y and finding for each y the value of (10 y – 20). From
the different values of (10y – 20) you obtain, do you see a solution to 10y – 20 = 50?
If there is no solution, try giving more values to y and find whether the condition
10y – 20 = 50 is met.

WHAT EQUATION IS?
In an equation there is always an equality sign. The equality sign shows that the value of
the expression to the left of the sign (the left hand side or LHS) is equal to
the value of the expression to the right of the sign (the right hand side or RHS). In
equation (4.1), the LHS is (4x + 5) and the RHS is 65. In equation (4.2), the LHS is
(10y – 20) and the RHS is 50.
If there is some sign other than the equality sign between the LHS and the RHS, it is
not an equation. Thus, 4x + 5 > 65 is not an equation.
It says that, the value of (4x + 5) is greater than 65.
Similarly, 4x + 5 < 65 is not an equation. It says that the value of (4x + 5) is smaller
than 65.

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