f(4) = 0
f'(4) = 0
f"(8/3) = 0
f'(8/3) = -4/3
64·a + 16·b + 4·c + d = 0
48·a + 8·b + c = 0
16·a + 2·b = 0
64/3·a + 16/3·b + c = -4/3
f(x) = 0,25·x^3 - 2·x^2 + 4·x
f'(x) = 0,75·x² - 4·x + 4
f''(x) = 1,5·x - 4
f'''(x) = 1,5
~plot~ 0,25*x^3-2*x^2+4*x;-4/3*(x-8/3)+32/27 ~plot~