GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2

   

Gujarat Board GSEB Textbook Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2 Textbook Questions and Answers.

Gujarat Board Textbook Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2

GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2

Question 1.
Using laws of exponents, simplify and write the answer in exponential form:
(i) 3² x 34 x 38
(ii) 615 ÷ 610
(iii) a3 x a2
(iv) 7x x 72
(v) (52)3 ÷ 53
(vi) 25 x 55
(vii) a4 x b4
(viii) (34)3
(ix) (220 ÷ 215) x 23
(x) 8t ÷ 82
Solution:
(i) 3² x 34 x 38
We have: 3² x 34 x 38 = 32+4+8 (∵ am x an x ar = am+n+r)
= 314
Thus, 32 x 34 x 38 = 314

(ii) 615 ÷ 610
We have: 615 ÷ 610 = 615-10 = 65 (∵ am ÷ an = am-n )
Thus, 615 ÷ 610 = 65

(iii) a3 x a2
We have: a3 x a2 = a3+2 = a5 (∵ am x an = am+n)
Thus, a3 x a2= a5

(iv) 7x x 72:
We have: 7x x 72 = 7x+2 (∵ am x an = am+n)
Thus, 7x x 72= 7x+2

(v) (5²)3 .÷ 53:
We have: (52)3 + 53 = 52×3 ÷ + 53
∵ [ (am)n = amn ]
= 56 ÷ 53
56-3 = 53 (∵ am ÷ an = am-n)
Thus, (5²)³ ÷ 5³ = 53

(vi) 25x 55:
We have: 25 x 55 = (2 x 5)5 = (10)5 (∵ am x an = (ab)m)
Thus, 25 x 55 = 105

(vii) a4 x b4:
We have: a4 x b4 = (ab)5 [ ∵ am x an = (ab)m ]
Thus, a4 x b4 = (ab)4

(viii) (34)3:
We have: (34)3 = 34×3 = 312 [ ∵ am x an = (ab)m ]
Thus, (34)3 = 312

(ix) (220 ÷ 215) x 23:
We have: (220 ÷ 215) x 23 (∵ am ÷ an = am-n)
= (25) x 23
= 25 x 23
= 25+3 (∵ am x an = am+n)
= 28
= 28
Thus, (220 + 215) x 23 = 28

(x) 8t ÷ 82:
We have:
8t ÷ 82 = 8t-2 (∵ am ÷ an = am-n)
Thus, 8t ÷ 82 = 8t-2

GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2

Question 2.
Simplify and express each of the following in exponential form:
(i) \(\frac{2^{3} \times 3^{4} \times 4}{3 \times 32}\)
(ii) [(5²)³ x 54] ÷ 57
(iii) 254 ÷ 53
(iv) \(\frac{3 \times 7^{2} \times 11^{8}}{21 \times 11^{3}}\)
(v) \(\frac{3^{7}}{3^{4} \times 3^{3}}\)
(vi) 2° + 3° + 4°
(vii) 2° x 3° x 4°
(viii) (3° + 2°) x 5°
(ix) \(\frac{2^{8} \times a^{5}}{4^{3} \times a^{3}}\)
(x) \(\left[\frac{a^{5}}{a^{3}}\right]\)
(xi) \(\frac{4^{5} \times a^{8} b^{3}}{4^{5} \times a^{5} b^{2}}\)
(xii) (2³ x 2)²
Solution:
GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2 1

(vi) 2° + 3° + 4°:
Since a° = 1
∴ 2° = 1, 3° = 1 and 4° = 1
We have : 2° + 3° + 4° = 1 + 1 + 1 = 3

(vii) 2° x 3° x 4°:
Since a° = 1
∴ 2° = 1, 3° = 1 and 4° = 1
Now, 2° x 3° x 4° = 1 x 1 x 1 = 1

(viii) (3° + 2°) x 5°:
We have o° = 1
(3° + 2°) x 5° = (1 + 1) x 1
= 2 x 1 = 2

(ix) \(\frac{2^{8} \times a^{5}}{4^{3} \times a^{3}}\)
GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2 2

(xii) (2³ x 2)²:
We have: (2³ x 2)² = (23+1 )² (∵ am x an = am )
= (24
= 24 x 2 (∵ (am)n = amn )
= 28

GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2

Question 3.
Say true or false and justify your answer:
(i) 10 x 1011 = 10011
(ii) 23 > 5²
(iii) 2³ x 3² = 65
(iv) 3° = (1000)°
Solution:
(i) 10 x 1011 = 10011
∵ 10 x 1011 = 101 + 11 = 1012
But 1012 ≠ 10011
∴ 10 x 1011 ≠ 10011
i.e. The statement 10 x 1011 = 10011 is false.

(ii) 23 > 52
∵ 23 = 2 x 2 x 2 = 8
5² = 5 x 5 = 25
and 8 < 25, i.e. 2² < 5²
Thus, the statement 23 > 5² is false.

(iii) 2³ x 3² = 65
∵ 2³ x 3² = 2 x 2 x 2 x 3 x 3 = 72
and 65 = 6 x 6 x 6 x 6 x 6 = 7776
Also 72 ≠ 7776
∴ 2³ x 3² ≠ 65
i.e. The statement 2³ x 3² = 65 is false

(iv) 3° = (1000)°
Since, 3° = 1 and (1000)° = 1
∴ 3° = (1000)° is a true statement.

Question 4.
Express each of the following as a product of prime factors only in exponential form:
(i) 108 x 192
(ii) 270
(iii) 729 x 64
(iv) 768
Solution:
(i) 108 x 192:
GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2 3
∵ 108 = 2 x 2 x 31 x 3 x 3
192 = 2 x 2 x 2 x 2 x 2 x 2 x 3
∴ 108 x 192 = (2 x 2 x 3 x 3 x 3) x (2 x 2 x 2 x 2 x 2 x 2 x 3)
= 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 3 x 3 x 3 x 3
= 28 x 34
Thus, 108 x 192 = 28 x 34

(ii) 270:
GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2 4
We have: 270 = 2 x 3 x 3 x 3 x 5
= 21 x 3³ x 51
= 2 x 3³ x 5
Thus, 270 = 2 x 3³ x 5

(iii) 729 x 64:
We have: 729 = 3 x 3 x 3 x 3 x 3 x 3
64 = 2 x 2 x 2 x 2 x 2 x 2
GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2 5
∴ 729 x 64 = (3 x 3 x 3 x 3 x 3 x 3) x (2 x 2 x 2 x 2 x 2 x 2)
= 36 x 26
Thus, 729 x 64 = 36 x 26

(iv) 768:
GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2 6
We have: 768 = 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 3
= 28 x 31
= 28 x 3
Thus, 768 = 28 x 3

GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2

Question 5.
Simplify:
(i) \(\frac{\left(2^{5}\right)^{2} \times 7^{3}}{8^{3} \times 7}\)
(ii) \(\frac{25 \times 5^{2} \times t^{8}}{10^{3} \times t^{4}}\)
(iii) \(\frac{3^{5} \times 10^{5} \times 25}{5^{7} \times 6^{5}}\)
Solution:
GSEB Solutions Class 7 Maths Chapter 13 Exponents and Powers Ex 13.2 7

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