Question by Lê Anh Duy

12/03/2018 at 15:32

- The fastest person who answer correctly will get 1 point/question/answer

- You can still answer my old question at https://e-learning.codienhanoi.edu.vn/discuss/member/leanhduy0206 and get point

THE QUESTION TODAY IS:

6) Find x that satisfy:

- \(x\in Q\), x² is a square number

- x² + 5 and x²- 5are also square number

Let's see who can solve this

Your IQ will be over 150 if you can

FC Alan Walker 16/03/2018 at 10:28

We have: \(x^2\) is a square number

\(\Rightarrow x\in Z\)

-C₁: \(x⋮3\)

\(\Rightarrow x^2\equiv0\) (mod 3)

\(\Rightarrow x^2+5\equiv2\) (mod 3) (Impossible because \(x^2+5\) is a square number)

-C₂: \(x⋮̸3\)

\(\Rightarrow x^2\equiv1\) (mod 3)

\(\Rightarrow x^2-5\equiv2\) (mod 3) (Impossible because \(x^2-5\) is a square number)

So can't find x.
Selected by MathYouLike
Lê Anh Duy 19/03/2018 at 13:44

Your answer is incorrect, try again
Lê Anh Duy 12/03/2018 at 15:35

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