Question

The student came to the conclusion that the system has infinitely many solutions, which is not correct. Describe the error was the student work being shown.

Answer 1

The student did not make use of the *other* equation. It is true that a single equation with two variables will have infinite solutions, but two equations with two unknowns, not always!

Answer 2

though the solving for "x" is correct, is only good if the substitution is done no unto itself, because that simply gives it a circular solution which will give that, but is only good if it's used on the other equation.