Plot these points in the graph:
f(x)=(x+1)(x-5)

graph based on step by step

Step-by-step explanation:

Graph the x intercepts, when x=0 set x+1=0 and x-5=0 and you get x=5 and x=-1, these are the points when y=0. then you can foil them out and see the way the parabola is structured, then you see that the middle of the intercepts is x=2, plug that into the equation either in intercept form of standard (foiled) and find the maximum/minimum

yes because there is exactly one y value for every x value

for function there can't be more than one value for every x value