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

Algebra.Com
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:
Answer by reviewermath(1029)   (Show Source): 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:
Answer by MathLover1(20849)   (Show Source): 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
..->.....




RELATED QUESTIONS

I need help with this equation: 1-2x/3 + x/2 = 1 When I tryed solving this problem I got (answered by blwinbbbles)
i am doing quadratic equation and i am lost right now my head hurts. someone explain... (answered by Alan3354)
I was wondering have do you solve this system using elimination x+y=2 x-y=4 I have tryed (answered by Alan3354)
Hi I have been trying to figure this out but it seems there are no examples in my book or (answered by Earlsdon)
I can't figure this out {{{2x^2-16x-18=0}}} I tried factoring by trinomials but I... (answered by minerva)
I need help this is the last question on my homework and i have been siting here for 30... (answered by jim_thompson5910)
Solving equations by factoring: 3zē=12z I know the answer is {0,4} from the back of the (answered by mananth,addingup)
I can't figure out the answer to this question - without solving or factoring, I must... (answered by stanbon)
I need help solving quadratic equations by factoring. The question I need help on is not... (answered by checkley75)