If x_2 – 3x + 1 = 0, then the value of x^3 + 1/{x^3} x is

RRB NTPC Mains or Stage 2 Model Paper 6 with solutions

Question : 39 of 119

Marks: +1, -0

x_2 – 3x + 1 = 0

, then the value of

x^3 + 1/{x^3} x

Solution:

(b)

x^2 – 3x + 1 = 0

⇒x^2 + 1 = 3x ⇒ x +1/x = 3

∴ x^3 +1/{x^ 3}=[x+1/x]^3-3x1 /x [x+1/x]

= 27 – 3 × 3 = 18

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