Given the parabola y =-2x -8x+9. State the Range. (draw a sketch if necessary)

Algebra and Trigonometry (6th Edition)
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ChapterP: Prerequisites: Fundamental Concepts Of Algebra
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### Question 6
Given the parabola \( y = -2x^2 - 8x + 9 \). State the Range. *(Draw a sketch if necessary)*

#### Explanation:
To determine the range of a quadratic function, it's helpful to identify the vertex of the parabola, especially since the function is written in standard form \( y= ax^2 + bx + c \). 

1. **Identify the coefficients:** In the given function \( y = -2x^2 - 8x + 9 \):
   - \( a = -2 \)
   - \( b = -8 \)
   - \( c = 9 \)

2. **Calculate the vertex:** The x-coordinate of the vertex of a parabola in standard form can be found using the formula \( x = -\frac{b}{2a} \). Substituting the values of \( a \) and \( b \):
   \[
   x = -\frac{-8}{2(-2)} = \frac{8}{-4} = -2
   \]

3. **Find the y-coordinate of the vertex:** Substitute \( x = -2 \) back into the original equation to find the y-coordinate.
   \[
   y = -2(-2)^2 - 8(-2) + 9 = -2(4) + 16 + 9 = -8 + 16 + 9 = 17
   \]

The vertex of the parabola is at \( (-2, 17) \). Since the coefficient of \( x^2 \) is negative (\( a = -2 \)), the parabola opens downwards, hence the vertex represents the maximum point.

4. **State the range:** 
   - The range includes all values of \( y \) that are less than or equal to the maximum value (the y-coordinate of the vertex). 
   \[
   \text{Range} = (-\infty, 17]
   \]

Drawing a sketch would show a downward-opening parabola with its highest point at (–2, 17).

#### Graph/Diagram:
If necessary, a simple sketch of the parabola would display the following:
   - A parabolic curve that opens downwards.
   - The vertex at (-2, 17), indicating the highest point on the graph.
   - The y-axis and x-axis to reference the position
Transcribed Image Text:### Question 6 Given the parabola \( y = -2x^2 - 8x + 9 \). State the Range. *(Draw a sketch if necessary)* #### Explanation: To determine the range of a quadratic function, it's helpful to identify the vertex of the parabola, especially since the function is written in standard form \( y= ax^2 + bx + c \). 1. **Identify the coefficients:** In the given function \( y = -2x^2 - 8x + 9 \): - \( a = -2 \) - \( b = -8 \) - \( c = 9 \) 2. **Calculate the vertex:** The x-coordinate of the vertex of a parabola in standard form can be found using the formula \( x = -\frac{b}{2a} \). Substituting the values of \( a \) and \( b \): \[ x = -\frac{-8}{2(-2)} = \frac{8}{-4} = -2 \] 3. **Find the y-coordinate of the vertex:** Substitute \( x = -2 \) back into the original equation to find the y-coordinate. \[ y = -2(-2)^2 - 8(-2) + 9 = -2(4) + 16 + 9 = -8 + 16 + 9 = 17 \] The vertex of the parabola is at \( (-2, 17) \). Since the coefficient of \( x^2 \) is negative (\( a = -2 \)), the parabola opens downwards, hence the vertex represents the maximum point. 4. **State the range:** - The range includes all values of \( y \) that are less than or equal to the maximum value (the y-coordinate of the vertex). \[ \text{Range} = (-\infty, 17] \] Drawing a sketch would show a downward-opening parabola with its highest point at (–2, 17). #### Graph/Diagram: If necessary, a simple sketch of the parabola would display the following: - A parabolic curve that opens downwards. - The vertex at (-2, 17), indicating the highest point on the graph. - The y-axis and x-axis to reference the position
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