How do I create a quartic polynomial function that opens down, has a positive real triple zero and one negative real zero?
y = (x-a)(x-b)(x-c)(x-d)
y = -(x-a)(x-b)(x-c)(x-d)
0 < b = c = d -- Just pick a value > 0 amd use it three times.
a < 0 -- Just pick a value < 0.
a = -1 < 0
b = c = d = 1 > 0
y = -(x+1)(x-1)(x-1)(x-1)