Problem 31 - Introductory Algebra for College Students

Question

Graph the parabola whose equation is given $$y=x^{2}-1$$

Step-by-Step Solution

Answer

The graph of the parabola \(y=x^{2}-1\) opens upward, has its vertex at the point (0, -1), which is also the y-intercept, and the axis of symmetry at x=0.

Step 1: Identify the Vertex and Axis of Symmetry

In the given equation \(y=x^{2}-1\), it is in the form \(y=a(x-h)^{2}+k\), where (h,k) is the vertex of the parabola. Since there's no value subtracted from x directly, h=0. The value of k is -1. Thus, the vertex is at (0, -1). The axis of symmetry of the parabola is at x=h, hence at x=0.

Step 2: Plot the Vertex and the Axis of Symmetry

Plot the vertex (0, -1) on the coordinate plane. Draw a dotted line through the vertex to show the axis of symmetry which is x=0.

Step 3: Find and Plot the Y-Intercept

The y-intercept is found by setting x=0 in the equation. For the given equation, when x=0, \(y=(0)^{2}-1=-1\). So, the y-intercept is also at (0, -1). Mark this point on the graph.

Step 4: Identify Additional Points and Complete the Graph

To graph a parabola, it is helpful to have additional points. Choose a few values to the left and right of the axis of symmetry, calculate y-values by plugging in to the equation, and plot the points. The parabola is symmetrical about the axis, so points on either side should match up. Now, draw a smooth curve through the points to complete the graph.

Key Concepts

Vertex of a Parabola

In exploring the graph of a parabola, understanding the vertex is fundamental. The vertex is that special point where the parabola changes direction. It represents the maximum or minimum of the parabola, depending whether it opens upwards or downwards respectively. For the equation \(y = x^2 - 1\), it is in the standard form \(y = a(x - h)^2 + k\), where \((h, k)\) is the vertex. Given this parabolic equation doesn't show an \((x - h)\) part explicitly, our vertex's \(h\) value defaults to zero. The constant term \(-1\) is our \(k\), placing the vertex at \((0, -1)\).

Visualizing this on a graph, it's the point where the curve bottoms out since our parabola opens upwards, evidenced by the positive coefficient of \(x^{2}\). The vertex is the heart of the parabola, providing a reference point from which its shape can be fleshed out on a coordinate plane.

Axis of Symmetry

The axis of symmetry is as crucial as the contour of the parabola itself. It's an imaginary vertical line that passes through the vertex, forming a mirror line dividing the parabola into two symmetrical halves. For the equation \(y = x^2 - 1\), the axis of symmetry is found by identifying the \(x\) value of the vertex (\(h\)). In this case, since \(h\) is zero, the axis of symmetry is the vertical line where \(x = 0\), also known as the y-axis. This line is not only a powerful guide to plotting the shape of the graph but also simplifies solving parabolic equations by providing a symmetrical perspective.

Y-intercept

The y-intercept of a graph is located precisely where the graph crosses the y-axis. It's an important characteristic that can be quickly identified, as it corresponds to the output value when all input values are zero. In other words, to determine the y-intercept of the parabola described by \(y = x^2 - 1\), set \(x\) to zero and solve for \(y\). The calculation yields \(y = (0)^2 - 1\), which simplifies to \(-1\). Hence, our y-intercept is the point \((0, -1)\), coinciding with the vertex in this specific case. If the vertex and y-intercept align, it signifies an even further simplified structure to the parabola, making the graphing process more intuitive for both plotting and comprehension.

Visual learners and those working through mathematics problems benefit greatly from recognizing how the y-intercept serves as a starting point when sketching a graph from scratch.