If sum of the roots of the equation $5 x^{4} - k x^{3} + 8 x + 1 = 0$ is $6$ , then $k$ is equal to

6

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- 6

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- 30

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30

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Solution

The correct option is D $30$
Given equation is $5 x^{4} - k x^{3} + 8 x + 1 = 0$
Sum of the roots $= - \frac{coefficient of x^{3}}{coefficient of x^{4}}$
$= \frac{- (- k)}{5}$

$= \frac{k}{5}$

It is given that the sum of roots is $6$ .
Hence, $\frac{k}{5} = 6$
$k = 30$

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