Problem
NT-B1-M04-P005 Cannot Divide Without Checking
#5
★☆☆☆☆ Level 1 of 5
Prove that \(2x\equiv1\pmod4\) has no solutions.
The left side is always even.
The number \(2x\) is even, so modulo \(4\) it can have residue \(0\) or \(2\). Residue \(1\) is impossible. Also \(\gcd(2,4)=2\nmid1\), so there are no solutions.
Highlights the main trap of the module.