Chapter 8: Problem 24
Graph each quadratic function, and state its domain and range. $$g(x)=-x^{2}-1$$
Short Answer
Expert verified
Domain: \((-\infty, \infty)\). Range: \((-\infty, -1]\). Vertex: (0, -1).
Step by step solution
01
- Identify the Quadratic Function
The quadratic function given is \[ g(x) = -x^2 - 1 \]. This is a downward-opening parabola because the coefficient of \(x^2\) is negative.
02
- Find the Vertex
The vertex form of a quadratic function is \[ g(x) = a(x-h)^2 + k \]. In this case: \[ g(x) = -x^2 - 1 \]. The vertex \( (h, k) \) is at: \[ (0, -1) \].
03
- Identify the Axis of Symmetry
The axis of symmetry is a vertical line that goes through the vertex. For this function, the axis of symmetry is: \[ x = 0 \].
04
- Determine the Y-Intercept
The y-intercept is the point where the graph crosses the y-axis. To find it, set \( x = 0 \): \[ g(0) = -0^2 - 1 = -1 \]. So, the y-intercept is: \[ (0, -1) \].
05
- Determine the X-Intercepts
To find the x-intercepts, set \( g(x) = 0 \): \[ -x^2 - 1 = 0 \] This simplifies to: \[ -x^2 = 1 \] \[ x^2= -1 \]. Since there are no real solutions for \( x \) (the square root of a negative number is not real), there are no x-intercepts.
06
- Sketch the Graph
Using the vertex \( (0, -1) \), the axis of symmetry \( x = 0 \), and the y-intercept \( (0, -1) \), sketch the parabola opening downward.
07
- State the Domain
The domain of any quadratic function is all real numbers. So, the domain is: \[ (-\infty, \infty) \].
08
- State the Range
The range is the set of all possible values of \( g(x) \). Since the parabola opens downward with a maximum value at the vertex \( y = -1 \), the range is: \[ (-\infty, -1] \].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
quadratic function
A quadratic function is a type of polynomial function often written in the form \(f(x) = ax^2 + bx + c\). In our example, the quadratic function is \(g(x) = -x^2 - 1\).
vertex
The vertex is one of the key points of a quadratic function. It forms the peak or the lowest point of the parabola, known as either the maximum or minimum point.
axis of symmetry
The axis of symmetry is a vertical line that divides the parabola into two mirror images. This line always passes through the vertex.
y-intercept
The y-intercept is where the graph crosses the y-axis. This occurs when \(x\) equals 0.
x-intercepts
The x-intercepts are the points where the graph crosses the x-axis. This happens when \(g(x)\) equals 0.
domain and range
The domain of a quadratic function includes all real numbers, from negative infinity to positive infinity. The range of a parabola opening downward is from negative infinity up to the y-value of the vertex, and the range of a parabola opening upward is from the y-value of the vertex to positive infinity.