SOLUTION: What is the distance between the points where the graph of y = - 2x^2 - x + 15 crosses the x-axis?

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: What is the distance between the points where the graph of y = - 2x^2 - x + 15 crosses the x-axis?      Log On


   

Question 366783: What is the distance between the points where the graph of y = - 2x^2 - x + 15
crosses the x-axis?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
-2x%5E2+-+x+%2B+15
Find the roots, which are the x-axis crossings.
Use quadratic formula
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
a+=+-2
b+=+-1
c+=+15
x+=+%28-%28-1%29+%2B-+sqrt%28+%28-1%29%5E2-4%2A%28-2%29%2A15+%29%29%2F%282%2A%28-2%29%29+
x+=+%28+1+%2B-+sqrt%28+1+%2B+120+%29%29%2F+-4+
x+=+%281+%2B+11%29%2F-4
x+=+-3
and
x+=+%281+-+11%29%2F-4
x+=+5%2F2
The difference between the roots is 5%2F2+-+%28-3%29+=+11%2F2
Here's the plot:
+graph%28+400%2C+400%2C+-5%2C+5%2C+-5%2C+20%2C+-2x%5E2+-+x+%2B+15%29+