The Goal

Solve the following equation for y:

The Mistake

Find the algebra mistake:

(Roll the mouse over the algebra to see hints in red)

The Correction

(Roll the mouse over the area above to see the corrections in blue)

An Explanation

There are three mistakes, all sign errors. In the first step the sign of c is changed for no reason. In the second step the sign of the x² term is switched. In the third step the student forgot the ± in front of the square root.
Take great care with signs!