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

Question 135807: Using the equation: 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) (Show Source): You can put this solution on YOUR website!
THE BEST WAY IS TO GRAPH THIS EQUATION THUS:
(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) (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 , substitute 0 for y and solve:

Factor the left:

Using the zero product rule:
or , so or . That means the points of intersection are (0,0) and (4,0)
RELATED QUESTIONS
I hope someone can help me with this problem. I have the function f(x)=sqrt(x^2+81)-15. (answered by solver91311)
I thought I understood this theorem until I saw this problem, it is the only one on my... (answered by stanbon)
How to graph polynomials. Where do I start? I am lost on these two problems. I don't know (answered by stanbon)
I have a graphing project that I have to submit, but I am not quite sure I know how to do (answered by stanbon)
Hello I need some help with the problems below. I am not 100% sure how this site works... (answered by brianunlv,josmiceli)
Make a graph that shows when fahrenheit and celsius meet. I don't know what the x-axis or (answered by rfer)
how do you find where two lines cross with out graphing them; for example: y = 2x + 4 (answered by stanbon)
Which of the following expressions represents the product of 3 less than twice x and 2... (answered by mananth)
If one-fifth of the oil flows out every hour and 50,000 imperial gallons remain in the... (answered by Alan3354)