Math Problem Statement

The graph of a quadratic function having the form f(x) = ax^2 + bx + c passes through the points (0, -8), (3, 10), and (6, 34). What is the value of the function when x = -3?

Solution

We are given the quadratic function f(x)=ax2+bx+cf(x) = ax^2 + bx + c, and it passes through the points (0,8)(0, -8), (3,10)(3, 10), and (6,34)(6, 34). The question asks to find the value of the function when x=3x = -3.

Step 1: Set up the system of equations

Using the points provided, we can set up three equations for aa, bb, and cc.

  1. At x=0x = 0, f(0)=8f(0) = -8: a(0)2+b(0)+c=8    c=8a(0)^2 + b(0) + c = -8 \implies c = -8

  2. At x=3x = 3, f(3)=10f(3) = 10: a(3)2+b(3)+c=10    9a+3b8=10    9a+3b=18a(3)^2 + b(3) + c = 10 \implies 9a + 3b - 8 = 10 \implies 9a + 3b = 18 Simplifying this equation: 3a+b=6(Equation 1)3a + b = 6 \quad \text{(Equation 1)}

  3. At x=6x = 6, f(6)=34f(6) = 34: a(6)2+b(6)+c=34    36a+6b8=34    36a+6b=42a(6)^2 + b(6) + c = 34 \implies 36a + 6b - 8 = 34 \implies 36a + 6b = 42 Simplifying this equation: 6a+b=7(Equation 2)6a + b = 7 \quad \text{(Equation 2)}

Step 2: Solve the system of equations

Now, subtract Equation 1 from Equation 2: (6a+b)(3a+b)=76(6a + b) - (3a + b) = 7 - 6 3a=1    a=133a = 1 \implies a = \frac{1}{3}

Substitute a=13a = \frac{1}{3} into Equation 1: 3(13)+b=6    1+b=6    b=53\left(\frac{1}{3}\right) + b = 6 \implies 1 + b = 6 \implies b = 5

So, we now have:

  • a=13a = \frac{1}{3}
  • b=5b = 5
  • c=8c = -8

Step 3: Find f(3)f(-3)

Now that we know aa, bb, and cc, we can find the value of the function when x=3x = -3: f(3)=13(3)2+5(3)8f(-3) = \frac{1}{3}(-3)^2 + 5(-3) - 8 f(3)=13(9)158=3158=20f(-3) = \frac{1}{3}(9) - 15 - 8 = 3 - 15 - 8 = -20

Thus, the value of the function when x=3x = -3 is 20\boxed{-20}.

Would you like further details or explanations? Here are five related questions:

  1. How do you solve quadratic systems with three points?
  2. Can you explain how to eliminate variables in a system of equations?
  3. How does the quadratic formula relate to finding the coefficients of a parabola?
  4. What are other methods for solving systems of equations?
  5. Can the vertex form of a quadratic equation help in solving this?

Tip: Always start by solving for constants like cc first when the equation allows for an easy substitution.

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Math Problem Analysis

Mathematical Concepts

Quadratic Functions
Algebra
System of Equations

Formulas

Quadratic equation: f(x) = ax^2 + bx + c
Substitution of points into equations
System of linear equations for solving a, b, and c

Theorems

Method of solving systems of linear equations
Quadratic function theory

Suitable Grade Level

Grades 9-11