The function f is given in three equivalent forms. which form most quickly reveals the y-intercept?

a. f(x) = 1/2x² - 5x + 21/2
b. f(x) = 1/2(x - 3)(x - 7)
c. f(x) = 1/2(x - 5)² - 2

What is the y-intercept?

y-intercept = (0,_____)