Selina Textbook Solutions: Cubes and Cube Roots | Mathematics Class 8 ICSE PDF Download

 Page 1


4. Cubes and Cube-Roots 
(Including use of tables for natural numbers) 
EXERCISE 4(A) 
Question 1. 
Find the cube of : 
(i) 7 
(ii) 11 
(iii) 16 
(iv) 23 
(v) 31 
(vi) 42 
(vii) 54 
Solution: 
(i) (7)
3
 = 7 x 7 x 7 = 343 
(ii) (11)
3
 =11 x 11 x 11 = 1331 
(iii) (16)
3
 = 16 x 16 x 16 = 4096 
(iv) (23)
3
 = 23 x 23 x 23 = 12167 
(v) (31)
3
 = 31 x 31 x 31 = 29791 
(vi) (42)
3
 = 42 x 42 x 42 = 74088 
(vii) (54)
3
 = 54 x 54 x 54 = 157464 
Question 2. 
Find which of the following are perfect cubes : 
(i) 243 
(ii) 588 
(iii) 1331 
(iv) 24000 
(v) 1728 
(vi) 1938 
Solution: 
Page 2


4. Cubes and Cube-Roots 
(Including use of tables for natural numbers) 
EXERCISE 4(A) 
Question 1. 
Find the cube of : 
(i) 7 
(ii) 11 
(iii) 16 
(iv) 23 
(v) 31 
(vi) 42 
(vii) 54 
Solution: 
(i) (7)
3
 = 7 x 7 x 7 = 343 
(ii) (11)
3
 =11 x 11 x 11 = 1331 
(iii) (16)
3
 = 16 x 16 x 16 = 4096 
(iv) (23)
3
 = 23 x 23 x 23 = 12167 
(v) (31)
3
 = 31 x 31 x 31 = 29791 
(vi) (42)
3
 = 42 x 42 x 42 = 74088 
(vii) (54)
3
 = 54 x 54 x 54 = 157464 
Question 2. 
Find which of the following are perfect cubes : 
(i) 243 
(ii) 588 
(iii) 1331 
(iv) 24000 
(v) 1728 
(vi) 1938 
Solution: 
 
 
Page 3


4. Cubes and Cube-Roots 
(Including use of tables for natural numbers) 
EXERCISE 4(A) 
Question 1. 
Find the cube of : 
(i) 7 
(ii) 11 
(iii) 16 
(iv) 23 
(v) 31 
(vi) 42 
(vii) 54 
Solution: 
(i) (7)
3
 = 7 x 7 x 7 = 343 
(ii) (11)
3
 =11 x 11 x 11 = 1331 
(iii) (16)
3
 = 16 x 16 x 16 = 4096 
(iv) (23)
3
 = 23 x 23 x 23 = 12167 
(v) (31)
3
 = 31 x 31 x 31 = 29791 
(vi) (42)
3
 = 42 x 42 x 42 = 74088 
(vii) (54)
3
 = 54 x 54 x 54 = 157464 
Question 2. 
Find which of the following are perfect cubes : 
(i) 243 
(ii) 588 
(iii) 1331 
(iv) 24000 
(v) 1728 
(vi) 1938 
Solution: 
 
 
 
1938 = 2 x 3 x 17 x 19 
1938 is not a perfect cube. 
Question 3. 
Find the cubes of : 
(i) 2.1 
(ii) 0.4 
(iii) 1.6 
(iv) 2.5 
(v) 0.12 
(vi) 0.02 
(vii) 0.8 
Solution: 
Page 4


4. Cubes and Cube-Roots 
(Including use of tables for natural numbers) 
EXERCISE 4(A) 
Question 1. 
Find the cube of : 
(i) 7 
(ii) 11 
(iii) 16 
(iv) 23 
(v) 31 
(vi) 42 
(vii) 54 
Solution: 
(i) (7)
3
 = 7 x 7 x 7 = 343 
(ii) (11)
3
 =11 x 11 x 11 = 1331 
(iii) (16)
3
 = 16 x 16 x 16 = 4096 
(iv) (23)
3
 = 23 x 23 x 23 = 12167 
(v) (31)
3
 = 31 x 31 x 31 = 29791 
(vi) (42)
3
 = 42 x 42 x 42 = 74088 
(vii) (54)
3
 = 54 x 54 x 54 = 157464 
Question 2. 
Find which of the following are perfect cubes : 
(i) 243 
(ii) 588 
(iii) 1331 
(iv) 24000 
(v) 1728 
(vi) 1938 
Solution: 
 
 
 
1938 = 2 x 3 x 17 x 19 
1938 is not a perfect cube. 
Question 3. 
Find the cubes of : 
(i) 2.1 
(ii) 0.4 
(iii) 1.6 
(iv) 2.5 
(v) 0.12 
(vi) 0.02 
(vii) 0.8 
Solution: 
 
 
Page 5


4. Cubes and Cube-Roots 
(Including use of tables for natural numbers) 
EXERCISE 4(A) 
Question 1. 
Find the cube of : 
(i) 7 
(ii) 11 
(iii) 16 
(iv) 23 
(v) 31 
(vi) 42 
(vii) 54 
Solution: 
(i) (7)
3
 = 7 x 7 x 7 = 343 
(ii) (11)
3
 =11 x 11 x 11 = 1331 
(iii) (16)
3
 = 16 x 16 x 16 = 4096 
(iv) (23)
3
 = 23 x 23 x 23 = 12167 
(v) (31)
3
 = 31 x 31 x 31 = 29791 
(vi) (42)
3
 = 42 x 42 x 42 = 74088 
(vii) (54)
3
 = 54 x 54 x 54 = 157464 
Question 2. 
Find which of the following are perfect cubes : 
(i) 243 
(ii) 588 
(iii) 1331 
(iv) 24000 
(v) 1728 
(vi) 1938 
Solution: 
 
 
 
1938 = 2 x 3 x 17 x 19 
1938 is not a perfect cube. 
Question 3. 
Find the cubes of : 
(i) 2.1 
(ii) 0.4 
(iii) 1.6 
(iv) 2.5 
(v) 0.12 
(vi) 0.02 
(vii) 0.8 
Solution: 
 
 
 
Question 4. 
Find the cubes of : 
(i)  
(ii)  
(iii)  
(iv)  
(v)  
Solution: 
 
Question 5. 
Find the cubes of : 
(i) -3