# SOLUTION: I have tryed to figure out this equation. The book says it's solving Quadratic Equations by factoring. The answere is (-3,7) The computor says it's not possible to solve, Will you

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Question 639683: I have tryed to figure out this equation. The book says it's solving Quadratic Equations by factoring. The answere is (-3,7) The computor says it's not possible to solve, Will you show me how to solve it please
x^2-4x=21
Thank you!

Found 2 solutions by reviewermath, MathLover1:
You can put this solution on YOUR website!
 Solved by pluggable solver: SOLVE quadratic equation with variable Quadratic equation (in our case ) has the following solutons: For these solutions to exist, the discriminant should not be a negative number. First, we need to compute the discriminant : . Discriminant d=100 is greater than zero. That means that there are two solutions: . Quadratic expression can be factored: Again, the answer is: 7, -3. Here's your graph:

You can put this solution on YOUR website!

.........replace with
...group first two and second two terms together

...factor out from the first group and from the second group

now find solutions: recall, product is equal to zero if any of the factors is equal to zero
so, if
....->.....
or
..->.....