Find f(α) and f(β)

Find \( f(\alpha) \) and \( f(\beta) \)

Question:

If

\[ f(x)=64x^3+\frac1{x^3} \]

and \(\alpha,\beta\) are the roots of

\[ 4x+\frac1x=3, \]

then

(a) \(f(\alpha)=f(\beta)=-9\)
(b) \(f(\alpha)=f(\beta)=63\)
(c) \(f(\alpha)\ne f(\beta)\)
(d) none of these

Solution:

Given,

\[ 4x+\frac1x=3 \]

Cubing both sides,

\[ \left(4x+\frac1x\right)^3=3^3 \]

\[ 64x^3+\frac1{x^3} +12\left(4x\right)\left(\frac1x\right)\left(4x+\frac1x\right) =27 \]

\[ f(x)+48\left(4x+\frac1x\right)=27 \]

\[ f(x)+48(3)=27 \]

\[ f(x)=27-144 \]

\[ f(x)=-117 \]

Therefore,

\[ f(\alpha)=f(\beta)=-117 \]

None of the given options is correct.

\[ \boxed{\text{Correct Answer: (d)}} \]

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