NCERT Solutions Class 8 – Chapter 10 Exponents and Powers – Exercise 10.1
Question 1. Evaluate:
Solution:
(i) 3–2
3-2 = [Tex]\frac{1}{(3^2)} = \frac{1}{9} [/Tex] (Property used: a-n = [Tex]\frac{1}{a^n} [/Tex])
(ii) (– 4)– 2
(-4)-2 = [Tex]\frac{1}{(-4)^2} = \frac{1}{16} [/Tex] (Property used: a-n = [Tex]\frac{1}{a^n} [/Tex])
(iii) ([Tex]\frac{1}{2} [/Tex]) -5
([Tex]\frac{1}{2} [/Tex])-5 = (2)5 = 32 (Property used: [Tex](\frac{b}{a})^{-n} = \frac{a^n}{b^n} [/Tex])
Question 2. Simplify and express the result in power notation with a positive exponent.
Solution:
(i) (-4)5 ÷ (-4)8
= (-4)5-8 = (-4) -3 (Property used: am ÷ an= am-n)
= [Tex]\frac{1}{(-4)^3} [/Tex]
= [Tex]\mathbf{(\frac{1}{(-4)})^3}[/Tex]
(ii) [Tex](\frac{1}{2^3})^2[/Tex]
= [Tex]\frac{(1)^2}{(2^3)^2} [/Tex] (Property used: (am)n = am×n)
= [Tex]\frac{1}{2^6}[/Tex]
= [Tex]\mathbf{\frac{1}{2^6}}[/Tex]
(iii) (-3)4 × ([Tex]\frac{5}{3} [/Tex])4
= ((3)4 × [Tex]\frac{5^4}{3^4} [/Tex] (Property used: (a/b)n = an/ bn & (-a)n = an if a is positive number and n is even)
= 54
(iv) (3-7 ÷ 3-10) × 3-5
= 3 (-7-(-10)) × 3-5 (Property used: am ÷ an= am-n)
= 3 (-7+10) × 3-5
= 33 × 3-5
= 3 (3+(-5)) (Property used: am × an = a m + n)
= 3-2 (Property used: a-m =[Tex]\frac{1}{a^m} [/Tex])
= [Tex]\frac{1}{3^2}[/Tex]
= [Tex]\mathbf{\frac{1}{3^2}}[/Tex]
(v) 2-3 × (-7)-3
= (2 × (-7))-3 (Property used: am × bm = (a×b)m)
= (-14)-3 (Property used: a-m =[Tex]\frac{1}{a^m} [/Tex])
= [Tex]\frac{1}{(-14)^3}[/Tex]
=[Tex]\mathbf{\frac{1}{(-14)^3}}[/Tex]
Question 3. Find the value of
Solution:
(i) (30 + 4-1) × 22
= (1 + ([Tex]\frac{1}{4} [/Tex])) × 4 (a0 = 1 a ≠ 0)
= ([Tex]\frac{5}{4} [/Tex]) × 4
= 5
(ii) (2-1 × 4-1) ÷ 2-2
= (2 × 4)-1 ÷ [Tex]\frac{1}{2^2} [/Tex] (Property used: am × bm = (a×b)m)
= (8)-1 ÷ [Tex]\frac{1}{4}[/Tex]
= ([Tex]\frac{1}{8} [/Tex]) ÷ [Tex]\frac{1}{4}[/Tex]
=([Tex]\frac{1}{8} [/Tex]) × 4
= ([Tex]\frac{1}{2} [/Tex])
(iii) (1/2)-2 + (1/3)-2 + (1/4)-2
= 22 + 32 + 42 (Property used: [Tex](\frac{1}{a})^{-m} [/Tex] =am)
= 4 + 9 + 16
= 29
(iv) (3-1 + 4-1 + 5-1)0
= ([Tex]\frac{1}{3} + \frac{1}{4} + \frac{1}{5} [/Tex])0 (a0 = 1 (a ≠ 0)
= 0
(v) {([Tex]\frac{-2}{3} [/Tex])-2}2
= ([Tex]\frac{-2}{3} [/Tex]) -2×2 (Property used: (am)n = am×n)
= ([Tex]\frac{-2}{3} [/Tex])-4 = ([Tex]\frac{-3}{2} [/Tex])4 (Property used: (b/a)-n = an/bn)
= [Tex]\frac{3^4}{2^4}[/Tex]
= [Tex]\frac{81}{16}[/Tex]
Question 4. Evaluate
Solution:
(i) (8-1 × 53) / 2-4
= ([Tex]\frac{1}{8} [/Tex] × 125) / (2-4) (Property used: (b/a)-n = an/bn)
= ([Tex]\frac{1}{8} [/Tex]) × 125 × 24
= 250
(ii) (5-1 × 2-1) × 6-1
= (5 × 2)-1 × 6-1 (Property used: am × bm = (a×b)m)
= 10-1 × 6-1
= (10 × 6)-1 (Property used: am × bm = (a×b)m)
= 60-1
= [Tex]\frac{1}{60}[/Tex]
Question 5. Find the value of m for which 5m ÷ 5– 3 = 55
Solution:
5m-(– 3) = 55 (Property used: am ÷ an= am-n)
5m+3 = 55
m+3 = 5
m = 5-3
m = 2
Question 6. Evaluate
Solution:
(i) {([Tex]\frac{1}{3} [/Tex])-1 – ([Tex]\frac{1}{4} [/Tex])-1}-1
= (31 – 41) -1 (Property used: (1/a)-m = am)
= (-1)-1
= (1/(-1))1
= (-1)
(ii) ([Tex]\frac{5}{8} [/Tex])-7 × ([Tex]\frac{8}{5} [/Tex])-4
= ([Tex]\frac{5}{8} [/Tex])7 × ([Tex]\frac{8}{5} [/Tex])-4 (Property used: (b/a)-n = (a/b)n)
= ([Tex]\frac{8}{5} [/Tex]) 7+ (-4) (Property used: am × an = a m + n)
= ([Tex]\frac{8}{5} [/Tex])3 = 83/53
= [Tex]\frac{512}{125}[/Tex]
Question 7. Simplify
Solution:
(i) [Tex]\frac{(25 \times t^{-4})}{(5^{-3} \times 10 \times t^{-8})} [/Tex] (t ≠ 0)
= [Tex]\frac{(5^2 \times t^{-4})}{(5^{-3} \times 10 \times t^{-8})} [/Tex] (Property used: am ÷ an= am-n ) (25 = 52)
=[Tex]\frac{(5^{2-(-3)} \times t^{-4-(-8)})}{ 10}[/Tex]
= [Tex]\frac{(5^{5} \times t^{4})}{ 10}[/Tex]
= [Tex]\frac{(625 \times t^{4})}{ 2}[/Tex]
(ii) [Tex]\frac{(3^{-5} \times 10^{-5} \times 125)}{(5^{-7} \times 6^{-5})}[/Tex]
= [Tex]\frac{(3^{-5} \times (2\times 5)^{-5} \times 125)}{(5^{-7} \times (2 \times 3)^{-5})}[/Tex]
= [Tex]\frac{(3^{-5} \times 2^{-5}\times 5^{-5} \times 125)}{(5^{-7} \times 2^{-5} \times 3^{-5})} [/Tex] (Property used: (a×b)m = am × bm)
= (3-5-(-5) × 2-5-(-5) × 5 (-5)+3+7) (Property used: am ÷ an= am-n )
= (30 × 20 × 55) (a0 = 1 (a ≠ 0)
= 55
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