Math Problem Statement

Consider the function g(x) = -1/4x^2 - x + 4. What is the vertex, equation of the line of symmetry, maximum/minimum value, x-intercepts, and y-intercept of the function?

Solution

The function presented in the image is:

g(x)=14x2x+4g(x) = -\frac{1}{4}x^2 - x + 4

Let's break down the questions and solutions:

  1. Vertex of the function: The vertex of a quadratic function g(x)=ax2+bx+cg(x) = ax^2 + bx + c can be found using the formula for the xx-coordinate of the vertex:

    x=b2ax = -\frac{b}{2a}

    Here, a=14a = -\frac{1}{4} and b=1b = -1, so:

    x=12×14=2x = -\frac{-1}{2 \times -\frac{1}{4}} = -2

    To find the yy-coordinate of the vertex, substitute x=2x = -2 into the original equation:

    g(2)=14(2)2(2)+4=14(4)+2+4=1+2+4=5g(-2) = -\frac{1}{4}(-2)^2 - (-2) + 4 = -\frac{1}{4}(4) + 2 + 4 = -1 + 2 + 4 = 5

    Therefore, the vertex is (2,5)(-2, 5), which matches the correct answer in the image.

  2. Equation of the line of symmetry: The axis of symmetry is the vertical line that passes through the vertex. Since the xx-coordinate of the vertex is 2-2, the equation of the line of symmetry is:

    x=2x = -2

  3. Maximum or minimum value: Since the leading coefficient a=14a = -\frac{1}{4} is negative, the parabola opens downward, meaning the function has a maximum value at the vertex. The maximum value is the yy-coordinate of the vertex, which is 5.

  4. The x-intercepts: To find the x-intercepts, set g(x)=0g(x) = 0 and solve for xx:

    14x2x+4=0-\frac{1}{4}x^2 - x + 4 = 0

    Multiply through by 4 to eliminate the fraction:

    x24x+16=0-x^2 - 4x + 16 = 0

    Multiply by 1-1 to simplify:

    x2+4x16=0x^2 + 4x - 16 = 0

    Now, solve this quadratic equation using the quadratic formula:

    x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

    For a=1a = 1, b=4b = 4, and c=16c = -16:

    x=4±424(1)(16)2(1)=4±16+642=4±802x = \frac{-4 \pm \sqrt{4^2 - 4(1)(-16)}}{2(1)} = \frac{-4 \pm \sqrt{16 + 64}}{2} = \frac{-4 \pm \sqrt{80}}{2}

    Simplifying:

    x=4±452=2±25x = \frac{-4 \pm 4\sqrt{5}}{2} = -2 \pm 2\sqrt{5}

    This gives the x-intercepts as:

    x1=2+252.47,x2=2256.47x_1 = -2 + 2\sqrt{5} \approx 2.47, \quad x_2 = -2 - 2\sqrt{5} \approx -6.47

    Therefore, the correct x-intercepts are approximately (2.47,0)(2.47, 0) and (6.47,0)(-6.47, 0). It looks like you entered these values as (2.46,0)(2.46, 0) and (6.46,0)(-6.46, 0), which were marked incorrect likely because of rounding. Using more precise values would be correct.

  5. The y-intercept: The y-intercept occurs when x=0x = 0. Substituting into the equation for g(x)g(x):

    g(0)=14(0)20+4=4g(0) = -\frac{1}{4}(0)^2 - 0 + 4 = 4

    Therefore, the y-intercept is (0,4)(0, 4).


Would you like further details or have any questions about this solution?

Here are 5 related questions to consider:

  1. How do you determine whether a quadratic function has a maximum or minimum value?
  2. How would the vertex change if the coefficient of x2x^2 were positive instead of negative?
  3. Can the quadratic formula be used for any quadratic equation, and why?
  4. How would you graph the function g(x)g(x) based on the vertex, intercepts, and axis of symmetry?
  5. What is the significance of the discriminant b24acb^2 - 4ac in the quadratic formula?

Tip: Always be mindful of rounding errors when dealing with approximate answers. When in doubt, retain as many decimal places as possible before submitting final results.

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Math Problem Analysis

Mathematical Concepts

Quadratic Functions
Parabolas
Vertex
Intercepts

Formulas

Vertex formula: x = -b / 2a
Quadratic formula: x = (-b ± √(b² - 4ac)) / 2a
Standard form of a quadratic: g(x) = ax² + bx + c

Theorems

Quadratic Formula
Properties of Parabolas

Suitable Grade Level

Grades 9-12