Final answer:
To find the expression for a cubic function, you need to know the coordinates of three points on the graph of the function and solve a system of equations.
Step-by-step explanation:
An expression for a cubic function is of the form y = ax^3 + bx^2 + cx + d, where a, b, c, and d are constants. To find these constants, you need to know the coordinates of three points on the graph of the function. For example, if you have the points (x1, y1), (x2, y2), and (x3, y3), you can substitute these values into the equation and solve for a, b, c, and d using a system of equations. Once you have found the values for a, b, c, and d, you can write the expression for the cubic function.