SOLUTION: Hello! I am currently in algebra 1 at my middle school and I am trying to study for finals. I am having some trouble with quadratic equations and I hope that you can help. My

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: Hello! I am currently in algebra 1 at my middle school and I am trying to study for finals. I am having some trouble with quadratic equations and I hope that you can help. My      Log On


   

Question 311704: Hello!
I am currently in algebra 1 at my middle school and I am trying to study for finals. I am having some trouble with quadratic equations and I hope that you can help.
My teacher said to use the quadratic formula to find solutions and I have no idea how to do that.
Here is the problem:
(x-8)(x+1)=-20
Thank you very much for your time and effort.
Sincerely,
Lyn
Answer by Earlsdon(6294) About Me  (Show Source):
You can put this solution on YOUR website!
Solve:
%28x-8%29%28x%2B1%29+=+-20 First, multiply the two factors on the left side using the FOIL method.
x%5E2%2Bx-8x-8+=+-20 Simplify the left side.
x%5E2-7x-8+=+-20 Now add 20 to both sides to get the equation in standard form:ax%5E2%2Bbx%2Bc+=+0.
x%5E2-7x-8%2B20+=+0 Simplify.
x%5E2-7x%2B12+=+0 Now you can apply the quadratic formula: x+=+%28-b%2B-sqrt%28b%5E2-4ac%29%29%2F2a and, in your equation, a = 1, b = -7, and c = 12, so make the appropriate substitutions:
x+=+%28-%28-7%29%2B-sqrt%28%28-7%29%5E2-4%281%29%2812%29%29%29%2F2%281%29 Simplify.
x+=+%287%2B-sqrt%2849-48%29%29%2F2
x+=+%287%2B-sqrt%281%29%29%2F2
x+=+%287%2B1%29%2F2 or %287-1%29%2F2
highlight%28x+=+4%29 or highlight%28x+=+3%29