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Amit

· started a discussion

· 1 Months ago

Double ans (Question: 142948.0 )

Why the ans is not 14 (k^3+3k)

Question:
If 9x – \(\cfrac{9}{2x}\)= 18, then find the value of x3 – \(\cfrac{1}{8x^3}\) is: 
Options:
A) 9
B) 8
C) 27
D) 11
Solution:

9x – \(\cfrac{9}{2x}\) = 18 ⇒ x – \(\cfrac{1}{2x}\) = 2

cubing both sides,

x3 – \(\cfrac{1}{8x^3}\) – 3x. \(\cfrac{1}{2x}\) (x – \(\cfrac{1}{2x}\)) = 8

x3 – \(\cfrac{1}{8x^3}\) – \(\cfrac{3}{2}\) × 2 = 8

⇒ x3 - \(\cfrac{1}{8x^3}\) = 8 + 3 = 11 

Knowledge Expert

· commented

· 1 Months ago

Dear student
Given question and solution both
are correct.

Keep learning
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