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If the average of a number and its reciprocal is 2, then the average of its cube and its reciprocal is equal to:
Question

If the average of a number and its reciprocal is 2, then the average of its cube and its reciprocal is equal to:

A.

28

B.

26

C.

48

D.

36

Correct option is B


Given:
If the average of a number and its reciprocal is 2.
Formula used:
x^3+1/x^3 = 〖〖(x〗^3+1/x^3 )〗^3-3x (x+1/x)
Solution:
((x+1/x) )/2=2
⇒(x+1/x)=4
⇒ x^3+1/x^3 = 4^3 -3 x 4 =64 -12 = 52
∴ Average of x³ and 1/x^3 = (52 )/2= 26.

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