Find all values of $x$ such that $x^2 - 5x + 4 = 0 $. If you find more than one value, then list your solutions, separated by commas.

If you first factor this equation you find that its (x-4)(x-1) so x=4 and x=1.

If you check both you see that they are both true so the solutions are 4 and 1.