Answer:
The cubic function is f(x) = (27/32)·x - 3/32·x³ - -9/32·x² - 9/32
Explanation:
The given function is f(x) = a·x³ + b·x² + c·x + d
By differentiation, we have;
3·a·x² + 2·b·x + c = 0
3·a·(-3)² + 2·b·(-3) + c = 0
3·a·9 - 6·b + c = 0
27·a - 6·b + c = 0
3·a·(1)² + 2·b·(1) + c = 0
3·a + 2·b + c = 0
a·(-3)³ + b·(-3)² + c·(-3) + d = -3
-27·a + 9·b - 3·c + d = -3...(1)
a + b + c + d = 0...(2)
Subtracting equation (1) from equation (2) gives;
28·a - 8·b + 4·c = 3
Therefore, we have;
27·a - 6·b + c = 0
3·a + 2·b + c = 0
28·a - 8·b + 4·c = 0
Solving the system of equations using an Wolfram Alpha gives;
a = -3/32, b = -9/32, c = 27/32 from which we have;
a + b + c + d = 0 3 × (-3/32) + 2 × (-9/32) + (27/32) + d = 0
d = 0 - (0 3 × (-3/32) + 2 × (-9/32) + (27/32)) = -9/32
The cubic function is therefore f(x) = (-3/32)·x³ + (-9/32)·x² + (27/32)·x + (-9/32).