Chapter 1: Problem 12
State whether the graph of the function is a parabola. If the graph is a parabola, then find the parabola's vertex. \(y=3 x^{2}-6 x\)
Short Answer
Expert verified
The graph is a parabola with vertex \( (1, -3) \).
Step by step solution
01
- Identify the type of function
The given function is \(y = 3x^2 - 6x\). Notice the highest power of \(x\) is 2, which means this is a quadratic function. The graph of a quadratic function is always a parabola.
02
- Write the function in vertex form
To find the vertex of the parabola, we first need to rewrite the function in the vertex form, \(y = a(x-h)^2 + k\). We start by completing the square for the expression \(3x^2 - 6x\).
03
- Complete the square
First factor out the coefficient of \(x^2\) from the terms involving \(x\). \[ y = 3(x^2 - 2x) \] To complete the square, add and subtract \((\frac{2}{2})^2 = 1\) inside the parentheses: \[ y = 3(x^2 - 2x + 1 - 1) \] Group the perfect square trinomial and simplify: \[ y = 3((x-1)^2 - 1) \] Distribute the 3: \[ y = 3(x-1)^2 - 3 \] Now the function is in vertex form, \(y = 3(x-1)^2 - 3\).
04
- Identify the vertex
In the vertex form \(y = 3(x-1)^2 - 3\), the vertex \((h, k)\) can be directly read from the equation. Here, \(h = 1\) and \(k = -3\). Therefore, the vertex of the parabola is at \((1, -3)\).
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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 any function that can be written in the form: \[ y = ax^2 + bx + c \]The highest degree term is \(x^2\), which makes it quadratic. These functions generate graphs that are parabolas. Notice the function given in the exercise is: \[ y = 3x^2 - 6x \]Here, \( a = 3 \), \( b = -6 \), and \( c = 0 \).This confirms it's a quadratic function and the graph will be a parabola. Quadratic functions have several important properties, such as:
- Symmetry: The graph is symmetric about a vertical line called the axis of symmetry.
- Parabolic shape: The graph is U-shaped, opening either up or down depending on the sign of a.
- Vertex: The highest or lowest point on the parabola, depending on whether it opens down or up, respectively.
completing the square
Completing the square is a method used to transform a quadratic function into vertex form. This makes it easier to identify the vertex of the parabola.Let's break down the process:
- Step 1: Start with the quadratic expression \(3x^2 - 6x\).
- Step 2: Factor out the coefficient of \(x^2\) from terms involving \(x\): \(3(x^2 - 2x)\).
- Step 3: Adjust within the parentheses to create a perfect square trinomial. Add and subtract \((\frac{2}{2})^2 = 1\): \(3(x^2 - 2x + 1 - 1)\).
- Step 4: Group the perfect square trinomial \((x - 1)^2\) and simplify: \(3((x-1)^2 - 1)\).
- Step 5: Distribute the 3 to get the final vertex form: \(3(x-1)^2 - 3\).
vertex form
The vertex form of a quadratic function is expressed as: \[ y = a(x-h)^2 + k \]Here, \(h, k\) are the coordinates of the vertex of the parabola. It shows directly how the parabola is shifted from the origin. In our example, converting \(y = 3x^2 - 6x\) to vertex form gave us:\[ y = 3(x-1)^2 - 3 \]From this vertex form, we identify the vertex as \((1, -3)\). This makes it very easy to graph the parabola, as you now know:
- The vertex is at \((1, -3)\).
- The axis of symmetry is the vertical line \(x = 1\).
- The parabola opens upwards because the coefficient of \((x-1)^2\) is positive (i.e., \(a = 3\)).