RS Aggarwal Class 8 Math Fourth Chapter Cubes and Cube Roots Exercise 4B Solution

RS Aggarwal Class 8 Math Fourth Chapter Cubes and Cube Roots Exercise 4B Solution

EXERCISE 4B

Find the value of each of the following using the short-cut method:

(1) (25)3

Solution: Here, a = 2 and b = 5

       a2

×a

a3

       a2

×3b

3a2b

         b2

×3a

3ab2

        b2

×b

b3


 

      4

    × 2

8
    +7

15

             4

× 15

60

        + 16

76

     25

    × 6

150

 +12

162

        25

       × 5

125

 

 

∴ (25)3 = 15625

(2) (47)3

Solution: Here, a = 4 and b = 7

       a2

×a

a3

       a2

×3b

3a2b

         b2

×3a

3ab2

        b2

×b

b3


 

      16

        × 4

64
   +39

103

           16

× 21

336

        + 62

398

     49

  × 12

588

 +34

622

        49

       × 7

343

 

∴ (47)3 = 103823

(3) (68)3

Solution: Here, a = 6 and b = 8

       a2

×a

a3

       a2

×3b

3a2b

         b2

×3a

3ab2

        b2

×b

b3

 

      36

        × 6

216
   + 98

314

           36

× 24

864

      + 120

984

     64

  × 18

1152

 +51

1203

        64

       × 8

512

 

∴ (68)2 = 314432

(4) (84)3

Solution: here, a = 8 and b = 4

       a2

×a

a3

       a2

×3b

3a2b

         b2

×3a

3ab2

        b2

×b

b3

 

      64

        × 8

512
   + 80

592

           64

× 12

768

         + 39

807

     16

  × 24

384

   +6

390

        16

       × 4

64

 

∴ (84)3 = 592704

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