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Go do modulus (Posted on 2021-01-02) Difficulty: 2 of 5
Find all pairs (x,y) of positive integers that satisfy 2x+17=y4

No Solution Yet Submitted by Danish Ahmed Khan    
Rating: 4.0000 (1 votes)

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Question re: Solution | Comment 6 of 8 |
(In reply to Solution by Brian Smith)

BS, you say "This makes sense only when the equation is 0+1=1. Thus, x is even and y is odd."

In other words, 2^x=0(mod 4), and: y^4=1(mod 4)
It is quite true that y^4=1(mod 4) => y is ODD.
BUT, 2^x=0(mod4) is satisfied whenever x is any integer >=2, which covers ODD INTEGERS such as 3, 5, 7, ....etc. VIS-A-VIS THE EVEN INTEGERS.
Consequently, I fail to understand  the avenue whereby you have derived that x MUST BE EVEN.

Edited on December 17, 2021, 10:13 pm
  Posted by K Sengupta on 2021-12-17 22:12:43

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