Sunday, November 15, 2026

2026/092) Solve $x^2-2x + 2 \equiv 0 \pmod 5$


 We have 

$x^2-2x + 2 \equiv 0 \pmod 5$

$=>x^2 -2x + 1 + 1 \equiv 0 \pmod 5$ to make square on left side

$=>(x-1)^2 + 1 \equiv 0 \pmod 5$

$=>(x-1)^2 + 1 \equiv 0 \pmod 5$

$=>(x-1)^2  \equiv 4 \pmod 5$

Working in mod 5 we have

$0^2 \equiv 0 \pmod 5$

$1^2 \equiv 1 \pmod 5$

$2^2 \equiv 4 \pmod 5$

$3 \equiv 4 \pmod 5$

$4^2 \equiv 1 \pmod 5$

 So we have 

$x-1 \equiv 2\pmod 5$ or $x-1 \equiv 3 \pmod 5$

Or $ x \equiv 3 \pmod 5 $ or $x \equiv 4 \pmod 5$

  

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