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Introduction

If x2 + 5 =...

Question

If $(x^{2} + 5) = 7$ and $(x^{2} + 5) k = 21$ , find the value of $k$ .

A

3

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B

6

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C

7

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D

5

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Solution

The correct option is A $3$
We have $(x^{2} + 5) = 7$
$\Rightarrow x^{2} = 7 - 5$
$\Rightarrow x^{2} = 2$
Also we have $(x^{2} + 5) k = 21$ ....(i)
Put the value of $x^{2} = 2$ in equation (i)
$\Rightarrow (2 + 5) k = 21$
$\Rightarrow 7 k = 21$
$\Rightarrow k = \frac{21}{7} = 3$

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