Math Problem Statement

The equation provided is f(x) = ax^2 + bx + 3, with the conditions f'(3) = 4 and f(3) = 45. Find a and b.

Solution

The equation in the image provided is:

f(x)=ax2+bx+3f(x) = ax^2 + bx + 3

The conditions given are:

  1. f(3)=4f'(3) = 4
  2. f(3)=45f(3) = 45

We need to find the values of aa and bb.

Step 1: Derive the equation for f(x)f'(x)

The derivative of f(x)f(x) with respect to xx is:

f(x)=2ax+bf'(x) = 2ax + b

Step 2: Use the given condition f(3)=4f'(3) = 4

Substitute x=3x = 3 into f(x)f'(x):

f(3)=2a(3)+b=4f'(3) = 2a(3) + b = 4 6a+b=4(Equation 1)6a + b = 4 \quad \text{(Equation 1)}

Step 3: Use the given condition f(3)=45f(3) = 45

Substitute x=3x = 3 into f(x)f(x):

f(3)=a(32)+b(3)+3=45f(3) = a(3^2) + b(3) + 3 = 45 9a+3b+3=459a + 3b + 3 = 45 9a+3b=42(after subtracting 3 from both sides)9a + 3b = 42 \quad \text{(after subtracting 3 from both sides)} 3a+b=14(Equation 2, after dividing by 3)3a + b = 14 \quad \text{(Equation 2, after dividing by 3)}

Step 4: Solve the system of equations

We have two equations:

  1. 6a+b=46a + b = 4
  2. 3a+b=143a + b = 14

Now, subtract Equation 2 from Equation 1:

(6a+b)(3a+b)=414(6a + b) - (3a + b) = 4 - 14 3a=103a = -10 a=103a = -\frac{10}{3}

Step 5: Substitute aa back into one of the equations

Substitute a=103a = -\frac{10}{3} into Equation 2:

3(103)+b=143\left(-\frac{10}{3}\right) + b = 14 10+b=14-10 + b = 14 b=24b = 24

Final Answer:

  • a=103a = -\frac{10}{3}
  • b=24b = 24

Would you like more details or have any questions? Here are five related questions to explore:

  1. How would you graph the function f(x)=ax2+bx+3f(x) = ax^2 + bx + 3 with the values of aa and bb found?
  2. What does the derivative f(x)=2ax+bf'(x) = 2ax + b represent in terms of the slope of the curve?
  3. How would the value of f(x)f'(x) change if aa and bb were different?
  4. Can you determine the vertex of the quadratic function using the values of aa and bb?
  5. How would you solve for aa and bb if the function was cubic instead of quadratic?

Tip:

When solving systems of equations, substitution or elimination methods can both be effective.

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Math Problem Analysis

Mathematical Concepts

Quadratic Functions
Derivatives
System of Equations

Formulas

f(x) = ax^2 + bx + 3
f'(x) = 2ax + b

Theorems

Derivative of a quadratic function
Solving a system of linear equations

Suitable Grade Level

Grade 10-12