If $\alpha, \beta, \gamma$ are the roots of the equation $x^3 + 4x + 1 = 0$, then $(\alpha + \beta)^{-1} + (\beta + \gamma)^{-1} + (\gamma + \alpha)^{-1} =$
A4
B2
C3
D5
Answer & Solution
Correct answer: A. 4
Using Vieta's formulas for $x^3+0x^2+4x+1=0$,
$$\alpha+\beta+\gamma=0$$
$$\alpha\beta+\beta\gamma+\gamma\alpha=4$$
$$\alpha\beta\gamma=-1$$
Now,
$$\alpha+\beta=-\gamma,\quad \beta+\gamma=-\alpha,\quad \gamma+\alpha=-\beta$$
So the required sum is
$$-\left(\frac{1}{\alpha}+\frac{1}{\beta}+\frac{1}{\gamma}\right)$$
Further,
$$\frac{1}{\alpha}+\frac{1}{\beta}+\frac{1}{\gamma}=\frac{\alpha\beta+\beta\gamma+\gamma\alpha}{\alpha\beta\gamma}=\frac{4}{-1}=-4$$
Hence the value is
$$4$$
Checking the options, this matches $\text{(A)}$.
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