If $(x + 3)$ and $(x^{2} + 5 x + 7)$ are factors of the polynomial $P (x) = a x^{3} + b x^{2} + c x + d$ , then find $b$ .

1

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8

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21

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22

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Solution

The correct option is B $8$
As $(x + 3)$ and $(x^{2} + 5 x + 7)$ are the factors of $P (x)$
$\Rightarrow P (x) = (x + 3) {(x}^{2} + 5 x + 7) \Rightarrow P (x) = x^{3} + 5 x^{2} + 7 x + 3 x^{2} + 15 x + 21 \Rightarrow P (x) = x^{3} + 8 x^{2} + 22 x + 21$
Comparing with the given polynomial $P (x)$
We get $b = 8$
So option $B$ is correct.

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