The Goal

Solve the following equation for y:

The Mistake

Find the algebra mistake:

Need a hint? Look carefully at the red part of the algebra:

The Correction

An Explanation

The mistake was in canceling the "y" from both sides, despite the fact that on the left side the term is y and on the right side it is -y. To cancel from both sides the terms must be equal (including the same coefficients). "The Correction" shows how to solve the equation: bring all terms to one side and then factor.
(If it is not apparent how to factor a quadratic, then solve by completing the square or by using the quadratic formula.)