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2 Answers

Best answer
26 votes
26 votes
$x = \sqrt{12 + x}$

$\implies x^2 = 12 + x$

$\implies x^2 - x - 12 = 0$

$\implies (x-4) (x+3) = 0$

$\implies x = 4 \text{ or } x = -3$

Correct Answer: $C$
edited by
4 votes
4 votes

there is a really interesting math trick behind it.

If you see a question like this take out the number inside it (in this case is 12)

Take consecutive numbers such as:

$n(n+1)=12$

Always remember that the answer is $n+1$

solve it you get $n=3$ and $n+1=4$

so 4 is the answer.

 

Assume that there is $"-"$ instead of positive then answer would be $n$.

[If we solve by equation then it would be $x^{2}+x-12=0$ giving $x = 3$

 

 

Answer:

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