Common Algebra Mistakes
Example: Solving a Quadratic Equation

The Goal

Solve the following equation for y:


The Mistake

Find the algebra mistake:


(Roll the mouse over the algebra to see a hint in red)

The Correction


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

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.)

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