Math Problem Statement

Identify the vertex, the axis of symmetry, the maximum or minimum value, and the range of the parabola: y = -x^2 - 8x - 15

Solution

The equation given in the image is:

y=x28x15y = -x^2 - 8x - 15

This is a quadratic equation representing a parabola. Let's break down the information requested.

1. Vertex

The vertex of a parabola given by the form y=ax2+bx+cy = ax^2 + bx + c can be found using the formula for the x-coordinate of the vertex:

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

Here, a=1a = -1 and b=8b = -8. Substituting these values:

x=(8)2(1)=82=4x = \frac{-(-8)}{2(-1)} = \frac{8}{-2} = -4

Now, substitute x=4x = -4 back into the equation to find the y-coordinate:

y=(4)28(4)15=16+3215=1y = -(-4)^2 - 8(-4) - 15 = -16 + 32 - 15 = 1

Thus, the vertex is:

(4,1)(-4, 1)

2. Axis of Symmetry

The axis of symmetry is a vertical line that passes through the vertex. Since the x-coordinate of the vertex is 4-4, the equation for the axis of symmetry is:

x=4x = -4

3. Maximum or Minimum Value

Since the coefficient of x2x^2 (i.e., a=1a = -1) is negative, the parabola opens downwards. This means the vertex represents the maximum value of the parabola.

The maximum value is the y-coordinate of the vertex, which is:

11

4. Range of the Parabola

Since the parabola opens downwards, the range is all values of yy less than or equal to the maximum value. Therefore, the range is:

(,1](-\infty, 1]

Summary:

  • Vertex: (4,1)(-4, 1)
  • Axis of Symmetry: x=4x = -4
  • Maximum Value: 1
  • Range: (,1](-\infty, 1]

Let me know if you'd like more details or have any questions!

Here are 5 related questions to explore:

  1. How would the vertex change if the equation was y=x28x15y = x^2 - 8x - 15?
  2. What happens to the axis of symmetry if we add a constant to the entire equation?
  3. How do we determine whether a parabola opens upwards or downwards just by looking at the equation?
  4. Can the vertex represent a minimum in any case, and when would that happen?
  5. How does completing the square help in identifying the vertex form of a quadratic equation?

Tip: Always check the sign of aa in a quadratic equation to quickly determine if the parabola opens upwards (positive aa) or downwards (negative aa).

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Parabolas

Formulas

Vertex formula: x = -b / (2a)
Quadratic equation: y = ax^2 + bx + c

Theorems

The symmetry of parabolas
Maximum and minimum values of quadratic functions

Suitable Grade Level

Grades 9-12