Question 135807
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^2}}}, substitute 0 for y and solve:


{{{20x-5x^2=0}}}


Factor the left:
{{{5x(4-x)=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)