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×aa3 | a2×3b3a2b | b2×3a3ab2 | b2×bb3 |
| 4× 28 +715 | 4× 1560 + 1676 | 25 × 6150 +12162 | 25 × 5125 |
∴ (25)3 = 15625
(2) (47)3
Solution: Here, a = 4 and b = 7
| a2×aa3 | a2×3b3a2b | b2×3a3ab2 | b2×bb3 |
| 16× 464 +39103 | 16× 21336 + 62398 | 49 × 12588 +34622 | 49 × 7343 |
∴ (47)3 = 103823
(3) (68)3
Solution: Here, a = 6 and b = 8
| a2×aa3 | a2×3b3a2b | b2×3a3ab2 | b2×bb3 |
| 36× 6216 + 98314 | 36× 24864 + 120984 | 64 × 181152 +511203 | 64 × 8512 |
∴ (68)2 = 314432
(4) (84)3
Solution: here, a = 8 and b = 4
| a2×aa3 | a2×3b3a2b | b2×3a3ab2 | b2×bb3 |
| 64× 8512 + 80592 | 64× 12768 + 39807 | 16 × 24384 +6390 | 16 × 464 |
∴ (84)3 = 592704
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