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

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Question 1:

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

Answer 1:

${\left(25\right)}^3$
Here, a = 2 and b = 5
 
Using the formula $a^3+3a^{2}b+3a{b}^2+b^3$:

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

∴ ${\left(25\right)}^3$ = 15625

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

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Question 2:

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

Answer 2:

${\left(47\right)}^3$
Here, a = 4 and b = 7

Using the formula $a^3+3a^{2}b+3a{b}^2+b^3$:

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

∴ ${\left(47\right)}^3$ = 103823

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

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Question 3:

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

Answer 3:

${\left(68\right)}^3$
Here, a = 6 and b = 8

Using the formula $a^3+3a^{2}b+3a{b}^2+b^3$:

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

∴ ${\left(68\right)}^3$ = 314432

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

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Question 4:

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

Answer 4:

${\left(84\right)}^3$

Here, a = 8 and b = 4

Using the formula $a^3+3a^{2}b+3a{b}^2+b^3$:

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

∴ ${\left(84\right)}^3$ = 592704