a. Graph the function f(x) = 4 - x².

b. Identify the point (a, f(a)) at which the function has a tangent line with zero slope.

c. Consider the point (a, f(a)) found in part (b). Is it true that the secant line between (a - h, f(a - h)) and (a + h, f(a + h)) has slope zero for any value of h ≠ 0?