Math Problem Statement

The graph of the function f left parenthesis x right parenthesis equals ax squared plus bx plus c has its vertex at left parenthesis 0 comma 1 right parenthesis and passes through the point left parenthesis 1 comma 9 right parenthesis .  Find​ a, b, and c.

Solution

We are given the quadratic function f(x)=ax2+bx+cf(x) = ax^2 + bx + c and the following information:

  • The vertex is at (0,1)(0, 1), meaning f(0)=1f(0) = 1.
  • The graph passes through the point (1,9)(1, 9), meaning f(1)=9f(1) = 9.

Step 1: Use the vertex information

Since the vertex is (0,1)(0, 1), we can immediately determine cc because at x=0x = 0, f(0)=1f(0) = 1. So, using f(0)=ax2+bx+cf(0) = ax^2 + bx + c:

f(0)=a(0)2+b(0)+c=c=1f(0) = a(0)^2 + b(0) + c = c = 1

Thus, c=1c = 1.

Step 2: Use the point (1,9)(1, 9)

Next, we use the fact that the point (1,9)(1, 9) lies on the curve, so f(1)=9f(1) = 9. Substituting x=1x = 1 and f(1)=9f(1) = 9 into the equation:

f(1)=a(1)2+b(1)+1=9f(1) = a(1)^2 + b(1) + 1 = 9 a+b+1=9a + b + 1 = 9 a+b=8(Equation 1)a + b = 8 \quad \text{(Equation 1)}

Step 3: Use the vertex form condition

For a parabola with vertex (h,k)(h, k), the equation is given by:

f(x)=a(xh)2+kf(x) = a(x - h)^2 + k

In this case, the vertex is (0,1)(0, 1), so:

f(x)=a(x0)2+1=ax2+1f(x) = a(x - 0)^2 + 1 = ax^2 + 1

Thus, from the vertex form, we know b=0b = 0.

Step 4: Solve for aa

Now that we know b=0b = 0, we substitute it into Equation 1:

a+0=8    a=8a + 0 = 8 \implies a = 8

Final Answer:

Thus, the values of aa, bb, and cc are: a=8,b=0,c=1a = 8, \quad b = 0, \quad c = 1

The function is f(x)=8x2+1f(x) = 8x^2 + 1.

Would you like further clarification, or should I dive deeper into any part of this?


Here are 5 related questions for practice:

  1. What is the axis of symmetry of the function f(x)=8x2+1f(x) = 8x^2 + 1?
  2. How do you find the vertex of a quadratic function in standard form?
  3. If the function passed through (2,33)(2, 33) instead of (1,9)(1, 9), how would that affect the equation?
  4. Can a quadratic function have more than one vertex?
  5. What is the domain and range of the function f(x)=8x2+1f(x) = 8x^2 + 1?

Tip: The vertex form of a quadratic function is useful for finding the vertex directly from the equation.

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Math Problem Analysis

Mathematical Concepts

Quadratic Functions
Vertex Form
Parabolas

Formulas

General form of a quadratic function: f(x) = ax^2 + bx + c
Vertex form of a quadratic function: f(x) = a(x - h)^2 + k

Theorems

Vertex of a quadratic function occurs at (h, k) for vertex form
A point on the curve can be used to find constants in the quadratic equation

Suitable Grade Level

Grades 9-12