SOLUTION: Hi, please answer this question. I have: x^2-x-5=0. I know how to solve this using the quadratic equation method. The answers I get are (1+-sqrt(21))/2. But instead of using the

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: Hi, please answer this question. I have: x^2-x-5=0. I know how to solve this using the quadratic equation method. The answers I get are (1+-sqrt(21))/2. But instead of using the       Log On


   

Question 150829: Hi, please answer this question.
I have: x^2-x-5=0. I know how to solve this using the quadratic equation method. The answers I get are (1+-sqrt(21))/2.
But instead of using the quadratic formula, can't I just say:
x^2-x=5
x(x-1)=5
x=5 or x=6
How come this answer is different from the one using the quadratic formula???
Thank you.
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
You're thinking of the zero product property. The zero product property says that if AB=0, then A=0 or B=0

However, if you have A%2AB=C where in this case C%3C%3E0, you cannot say that A=C or B=C