The solution was wrong.
Not just a typo wrong. Fundamentally wrong. The transfer function denominator had a sign error. The root locus went unstable. It was as if someone had deliberately corrupted the file to punish cheats. The solution was wrong
Frustrated, Marco slammed the laptop shut. Then, slowly, he opened the textbook again. He re-derived the Laplace transform by hand. He checked the Routh array twice. At 2 a.m., he found his mistake: a missing negative sign in the feedback loop. Marco slammed the laptop shut. Then
Marco blinked. “So all those PDFs online…” The solution was wrong