SOLUTION: Using the equation: {{{y=20x-5x^2}}} How do you figure out where the graph will cross the axis? I know it will be in two places but I don't know how to figure it out. Thank you

Algebra ->  Graphs -> SOLUTION: Using the equation: {{{y=20x-5x^2}}} How do you figure out where the graph will cross the axis? I know it will be in two places but I don't know how to figure it out. Thank you      Log On


   

Question 135807: Using the equation: y=20x-5x%5E2 How do you figure out where the graph will cross the axis? I know it will be in two places but I don't know how to figure it out.
Thank you
Found 2 solutions by checkley77, solver91311:
Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
THE BEST WAY IS TO GRAPH THIS EQUATION THUS:
+graph%28+300%2C+200%2C+-6%2C+5%2C+-10%2C+10%2C+-5x%5E2+%2B20x%29+ (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, -5x^2 +20x).
THE ANSWERS ARE:(0,0) & (4,0) FOR THE 2 INTERSECTIONS WITH THE X AXIS.

Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!
The graph of an equation of the form y = f(x) intersects the x-axis whenever y = 0 because any point on the x-axis has and ordered pair in the form (x,0).

So, if y=20x-5x%5E2, substitute 0 for y and solve:

20x-5x%5E2=0

Factor the left:
5x%284-x%29=0

Using the zero product rule:
5x=0 or 4-x=0, so x+=+0 or x+=+4. That means the points of intersection are (0,0) and (4,0)