The *graph of a function* (and not an equation) f(x) crosses the x-axis for any value of x such that f(x) = 0. We call x a root of f(x) in that case.
The simplest function with roots at both x = 3 and x = -8 is
f(x) = (x - 3) (x + 8)
since
f(3) = (3 - 3) (3 + 8) = 0 • 11 = 0
and
f(-8) = (-8 - 3) (-8 + 8) = -11 • 0 = 0
