RS Aggarwal solution class 8 chapter 4 Cubes and Cube roots Exercise 4B

Exercise 4B

Page-66

Q1 | Ex-4B | Class 8 | RS AGGARWAL | Cubes and Cube roots | Chapter 4 | myhelper

Question 1:

Find the value of using the short-cut method:
(25)3

Answer 1:

253
Here, a = 2 and b = 5
 
Using the formula a3+3a2b+3ab2+b3:

     4
× 2
      4
×  15
     25
×  6
   25
×5
    8
 +7
      60
  + 16
   150
+  12
  125
    15       76    162  

253 = 15625


Q2 | Ex-4B | Class 8 | RS AGGARWAL | Cubes and Cube roots | Chapter 4 | myhelper

Question 2:

Find the value of using the short-cut method:
(47)3

Answer 2:

473
Here, a = 4 and b = 7

Using the formula a3+3a2b+3ab2+b3:

     16
× 4
      16
×  21
     49
×  12
   49
×7
    64
 +39
      336
  +   62
   588
+  34
  343
    103        398    622  

473 = 103823


Q3 | Ex-4B | Class 8 | RS AGGARWAL | Cubes and Cube roots | Chapter 4 | myhelper

Question 3:

Find the value of using the short-cut method:
(68)3

Answer 3:

683
Here, a = 6 and b = 8

Using the formula a3+3a2b+3ab2+b3:

     36
× 6
      36
×  24
     64
×  18
   64
×8
    216
 +  98
      864
  + 120
   1152
+    51
  512
     314        984    1203  

683 = 314432


Q4 | Ex-4B | Class 8 | RS AGGARWAL | Cubes and Cube roots | Chapter 4 | myhelper

Question 4:

Find the value of using the short-cut method:
(84)3

Answer 4:

843

Here, a = 8 and b = 4

Using the formula a3+3a2b+3ab2+b3:

     64
×   8
      64
×  12
     16
×  24
   16
× 4
    512
 +  80
    768
  + 39
   384
+    6
  64
    592      807    390  

843 = 592704

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