Square Root problem, take a look

[sreecharan]

Is sqrt(x) a prime number?

(1)|3x-7| = 2x+2

(2) x^2 = 9x



answer below




From statement one, we know that x must be 1 or 9. From statement two, we know that x must be 0 or 9. Thus, since both statements must be true, we can deduce that x must be 9. Therefore sqrt x = 3.


I dont get this, if x = 9 then sqrt x can be +3 or -3, so how is the answer C, I think it should be E.

[grockit_jake]

Techincally when you have an equation x^2 = 9, then x = +/-3.

For some reason, when you have rt9, the answer is only +3. There is some complex derivation for this that everyone forgets in 9th grade.

BUT the question is asking if sqrtx is prime. 3 is prime, so the answer is Yes. (C).

Negative numbers are technically not considered in prime question. Wording was confusing though, not the best Q.