Class 7 Maths Chapter 1 Exercise 1.2 Pdf Notes NCERT Solutions

Class 7 Maths Chapter 1 Integers Exercise 1.2 pdf notes:-

Class 7 Maths Chapter 1 Exercise 1.2 Pdf Notes

Exercise 1.2 Class 7 maths Chapter 1 Pdf Notes:-

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Introduction:-

Closure under Addition
We have learnt that sum of two whole numbers is again a whole number. For example,
17 + 24 = 41 which is again a whole number. We know that, this property is known as the
closure property for addition of the whole numbers.

Commutative Property
We know that 3 + 5 = 5 + 3 = 8, that is, the whole numbers can be added in any order. In
other words, addition is commutative for whole numbers.
Can we say the same for integers also?
We have 5 + (– 6) = –1 and (– 6) + 5 = –1
So, 5 + (– 6) = (– 6) + 5
Are the following equal?
(i) (– 8) + (– 9) and (– 9) + (– 8)
(ii) (– 23) + 32 and 32 + (– 23)
(iii) (– 45) + 0 and 0 + (– 45)
Try this with five other pairs of integers. Do you find any pair of integers for which the
sums are different when the order is changed? Certainly not. We say that addition is
commutative for integers.
In general, for any two integers a and b, we can say
a + b = b + a
 We know that subtraction is not commutative for whole numbers. Is it commutative
for integers?
Consider the integers 5 and (–3).
Is 5 – (–3) the same as (–3) –5? No, because 5 – ( –3) = 5 + 3 = 8, and (–3) – 5
= – 3 – 5 = – 8.
Take atleast five different pairs of integers and check this.
We conclude that subtraction is not commutative for integers.
1.3.4 Associative Property
Observe the following examples:
Consider the integers –3, –2 and –5.
Look at (–5) + [(–3) + (–2)] and [(–5) + (–3)] + (–2).
In the first sum (–3) and (–2) are grouped together and in the second (–5) and (–3)
are grouped together. We will check whether we get different results.

TRY THESE
In both the cases, we get –10.
i.e., (–5) + [(–3) + (–2)] = [(–5) + (–2)] + (–3)
Similarly consider –3 , 1 and –7.
( –3) + [1 + (–7)] = –3 + _ = _
[(–3) + 1] + (–7) = –2 + _ = _
Is (–3) + [1 + (–7)] same as [(–3) + 1] + (–7)?
Take five more such examples. You will not find any example for which the sums are
different. Addition is associative for integers.
In general for any integers a, b and c, we can say
a + (b + c) = (a + b) + c
1.3.5 Additive Identity
When we add zero to any whole number, we get the same whole number. Zero is an
additive identity for whole numbers. Is it an additive identity again for integers also?
Observe the following and fill in the blanks:
(i) (– 8) + 0 = – 8 (ii) 0 + (– 8) = – 8
(iii) (–23) + 0 = _ (iv) 0 + (–37) = –37 (v) 0 + (–59) = (vi) 0 + = – 43
(vii) – 61 + = – 61 (viii) + 0 = _

The above examples show that zero is an additive identity for integers.
You can verify it by adding zero to any other five integers.
In general, for any integer a
a + 0 = a = 0 + a

  1. Write a pair of integers whose sum gives
    (a) a negative integer (b) zero
    (c) an integer smaller than both the integers. (d) an integer smaller than only one of the integers.
    (e) an integer greater than both the integers.
  2. Write a pair of integers whose difference gives
    (a) a negative integer. (b) zero.
    (c) an integer smaller than both the integers. (d) an integer greater than only one of the integers.
    (e) an integer greater than both the integers
Answers

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