Find the Values of a and b in a piecewise function. Help please

In summary, to find the values of a and b that make the function f(x) differentiable, we set x=2 in the given equations and solve for a and b. The point where the definitions change is at x=2, so the derivatives must match up and the function must be continuous at that point. To ensure this, we differentiate f(x) in both regions (x>2 and x<2) and set the limits of the derivatives equal to each other.
  • #1
jbender
3
0
Find the values of a and b that make the function f(x) differentiable.



f(x)={ ax^3 + 1 , for x<2
{ b(x-3)^2 +10, for x is greater than or equal to 2



ax^3 + 1 = b(x-3)^2 +10
3ax^2 = 2b(x-3)
From here I'm unsure of where to go.
 
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  • #2
jbender said:
Find the values of a and b that make the function f(x) differentiable.



f(x)={ ax^3 + 1 , for x<2
{ b(x-3)^2 +10, for x is greater than or equal to 2



ax^3 + 1 = b(x-3)^2 +10
3ax^2 = 2b(x-3)
From here I'm unsure of where to go.

The two separate definitions are both continuous and differentiable on their separate domains, so you want to find a and b so that these functions are continuous and differentiable at the point where the definitions change. Where is that?
 
  • #3
The point where the definitions change is at x=2. Correct?
 
  • #5
That's certainly a good start! You have used the fact that the function must be continuous at x= 2 and the derivatives must "match up". (A derivative is not necessarily continuous but it must satisfy the "intermediate value property" so that is correct. But the point is that must be true at x= 2. Set x= 2 in your equations and you will have two linear equations to solve for a and b.
 
  • #6
This is my work for setting x=2 in the two given equations.
a(2)^3 +1 = b(2-3)^2 +10
8a+1 = b+10
b=8a-9

What equation do I substitute "b=8a-9" to solve for the value "a" ?
 
  • #7
f '(2) must exist. That means that [itex]\lim_{x\to2^+}f'(x)=\lim_{x\to2^-}f'(x)=f'(2)\,.[/itex]

Differentiate f(x) in both regions, x > 2, and x < 2 .
 

1. What is a piecewise function?

A piecewise function is a type of mathematical function that is defined by different rules or equations for different intervals or "pieces" of the input. It is often used to model real-world situations where different rules apply in different scenarios.

2. How do you find the values of a and b in a piecewise function?

The values of a and b in a piecewise function can be found by setting up and solving a system of equations. First, identify the different intervals or "pieces" of the function and write down the corresponding equations. Then, use the given information or conditions to set up a system of equations and solve for a and b.

3. Can you give an example of a piecewise function?

Yes, an example of a piecewise function is: f(x) = { a + x, if x < 0; b - x, if x ≥ 0 }. This function has different rules for x < 0 and x ≥ 0, with a and b being the values that determine the output for each interval.

4. What is the importance of finding the values of a and b in a piecewise function?

Finding the values of a and b in a piecewise function is important because it allows us to accurately model and analyze real-world situations. These values represent important parameters or constants that determine the behavior of the function for different input values.

5. Are there any tips for solving a system of equations to find the values of a and b in a piecewise function?

Yes, a helpful tip is to carefully organize and label the different intervals or "pieces" of the function and the corresponding equations. This can make it easier to set up the system of equations and solve for the variables. Additionally, it can be helpful to check your solution by plugging in the values of a and b into the original function and making sure it satisfies all the given conditions.

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