If x-0 and 2 x -1-2 x -21- Find the value of 8 x 3-1-8 x3-4 MARKS-

Concept: 1 Mark Application: 3 Marks 2x + 1/2x = 21 8x^3 + 1/8x^3 = (2x)^3 + 1/(2x)^3 nbsp; nbsp;Use nbsp; a^3+b^3=(a+b)^3 3ab(a+b) =(2x + 1/2x)^3 3 ...

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Byju's Answer

Standard VII

Mathematics

(a-b)^2 Expansion and Visualisation

If x'=0 and 2...

Question

If $x \neq 0$ and $2 x + \frac{1}{2 x} = 21$ . Find the value of $8 x^{3} + \frac{1}{8 x^{3}}$ [4 MARKS]

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Solution

Concept: 1 Mark
Application: 3 Marks

$2 x + \frac{1}{2 x} = 21$

$8 x^{3} + \frac{1}{8 x^{3}} = (2 x)^{3} + \frac{1}{(2 x)^{3}}$
Use $a^{3} + b^{3} = (a + b)^{3} - 3 a b (a + b)$

$= {(2 x + \frac{1}{2 x})}^{3} - 3 (2 x) (\frac{1}{2 x}) (2 x + \frac{1}{2 x})$

$= (21)^{3} - 3 (21)$

$= 9261 - 63$

$= 9198$

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If x≠0 and 2x+12x=21. Find the value of 8x3+18x3 [4 MARKS]

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