Symbiosis National Aptitude Test SNAP 2015 Paper

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Question : 23 of 150

Marks: +1, -0

If

(x^4 + x^{–4})

= 322, then what is one of the value of

(x – x^{–1})

?

18
16
8
4

Solution:

Given,

x^4+1/x^4

= 322
⇒

(x^2+1/x^2)^2-2

= 322
⇒

(x^2+1/x^2)^2-2

= 324 =

18^2

⇒

x^2+1/x^2

= 18
⇒

(x-1/x)^2

+ 2 = 18
⇒

x-1/x

= 4

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