Solving for a Cubic Function with Given Points

It basically states that if a number is a root of a polynomial function, then (x-c) is a factor of the polynomial. So in this case, since f(-1)=f(0)=f(2)=0, then (x+1), (x), and (x-2) are all factors of the cubic function f(x). This is why we use the equation f(x) = a(x+1)(x)(x-2) to represent the function. The given value of f(1)=6 allows us to solve for the coefficient "a", giving us the complete expression for the cubic function. In summary, the equation f(x) = a(x+1)(x)(x-2) is used
  • #1
brycenrg
95
2

Homework Statement


Find an expression for a cubic function f if f(1)=6 and f(-1)=f(0)=f(2)=0


Homework Equations


I figured it out but I am not sure why we use the equation f(x) = a[x-(-1)](x-0)(x-2)


The Attempt at a Solution


Im assuming its because if u times that equation that is a cubic function, but does it have anything todo with f(-1)=f(0)=f(2)=0 ?
 
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  • #2
Certainly yes. Those f(c)=0 values mean that some binomial, x-c, is a factor of the function's expression or its definition. Your exercise gives you three of them and they are for a cubic function. The binomial factors will take care of your roots for your function. The coefficient, "a", is for accounting for the remainder in case you choose a value for x which is not a root. The given f(1)=6 helps you to find "a".
 
  • #3
@brycenbrg: Look up the factor theorem in your text or online.
 

1. How do I solve for a cubic function with given points?

To solve for a cubic function with given points, you can use the method of interpolation. This involves plugging in the given points into the general form of a cubic function, ax^3 + bx^2 + cx + d, and solving for the coefficients a, b, c, and d.

2. What are the steps involved in solving for a cubic function with given points?

The steps involved in solving for a cubic function with given points include:
1. Write out the general form of a cubic function: ax^3 + bx^2 + cx + d
2. Plug in the given points into the function and form a system of equations
3. Solve the system of equations to find the coefficients a, b, c, and d
4. Write out the final equation for the cubic function by replacing the coefficients in the general form
5. Check your solution by plugging in the given points and ensuring they satisfy the equation

3. Can I use a calculator to solve for a cubic function with given points?

Yes, you can use a calculator to solve for a cubic function with given points. However, it is recommended to also solve the equations manually to ensure accuracy and understanding of the process.

4. What if I do not have enough given points to solve for a cubic function?

If you do not have enough given points, it may not be possible to solve for a unique cubic function. In this case, you can estimate the missing points by using the method of interpolation or by graphing the given points and finding a curve that fits them best.

5. Can I use the same method to solve for higher order polynomial functions?

Yes, the same method of interpolation can be used to solve for higher order polynomial functions. However, the number of given points needed will increase with the degree of the polynomial. For a cubic function, at least 4 points are needed, whereas for a quartic function, at least 5 points are needed.

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