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Use a graphing utility to graph the quadratic function. Identify the vertex, axis of symmetry, and \(x\) -intercept(s). Then check your results algebraically by writing the quadratic function in standard form. $$f(x)=-\left(x^{2}+x-30\right)$$

Short Answer

Expert verified
The vertex of the function is at \(-0.5, 29.75\), the function has an axis of symmetry at \(x=-0.5\) and also intercepts the x-axis at \(x=-5\) and \(x=6\). The function in standard form is \(f(x)=-(x+0.5)^2+29.75\).

Step by step solution

01

Graph The Quadratic Function

Firstly, graph the quadratic function \(f(x)=-\left(x^{2}+x-30\right)\) using a graphing utility. The curve is an upside down parabola due to the negative leading coefficient.
02

Identify The Vertex

The vertex of a parabola is the point where the maximal or minimal value occurs. It can be found by using the formula \(h=-\frac{b}{2a}\), where \(h\) is the x-coordinate of the vertex and \(a\) and \(b\) are coefficients from the quadratic equation. The y-coordinate of the vertex is found by substituting \(h\) into the function. For \(f(x)=-\left(x^{2}+x-30\right)\), \(a=-1\) and \(b=1\), leading to \(h=-\frac{1}{2*(-1)}=-0.5\). Then substitute \(h\) into the function to get the y-coordinate: \(f(-0.5)=-\left(-0.5^{2}+0.5-30\right)=-(-29.75)\), therefore, the vertex is \(-0.5, -(-29.75)\), or \(-0.5, 29.75\).
03

Identify The Axis Of Symmetry

The axis of symmetry of the parabola is a vertical line that passes through the vertex. Hence, it's equation will be \(x=h\), where \(h\) is the x-coordinate of vertex. From step 2, \(h=-0.5\), therefore, the axis of symmetry is \(x=-0.5\).
04

Identify The X-Intercept(s)

The x-intercepts of the function are the points where the function equals zero. Therefore, we want to solve the equation \(0=-\left(x^{2}+x-30\right)\), which simplifies to \(x^{2}+x-30=0\). The solutions to this equation can be found by factoring or using the quadratic formula. When factoring, we want two numbers that multiply to -30 and add to 1, which are 6 and -5. Therefore, \(x^{2}+x-30=(x-6)(x+5)=0\), which gives solutions \(x=6\) and \(x=-5\). These are the x-intercepts of the function.
05

Write The Quadratic Function in Standard Form

The standard form of a quadratic function is \(f(x)=a(x-h)^{2}+k\), where \((h,k)\) is the vertex of the parabola. From above, the vertex is \(-0.5, 29.75\), so the standard form of the function would be \(f(x)=-1*(x-(-0.5))^{2}+29.75\), or after simplifying, \(f(x)=-(x+0.5)^2+29.75\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Vertex of a Parabola
Understanding the vertex of a parabola is crucial when graphing quadratic functions. The vertex is the highest or lowest point on the parabola, depending on whether the parabola opens upwards or downwards. In the context of the given exercise, the quadratic function has a negative leading coefficient, indicating that the parabola opens downwards, making the vertex the maximum point of the graph.

Algebraically, the vertex's x-coordinate (\( h \)) can be calculated using the formula \( h = -\frac{b}{2a} \), where \( a \) and \( b \) are the coefficients from the quadratic equation in the form \( ax^2 + bx + c \). After calculating \( h \) and evaluating the function at that point, we obtain both coordinates of the vertex. In our exercise, the vertex is at \( (-0.5, 29.75) \) which is a pivotal point for understanding the parabola’s shape and position on the graph.
Axis of Symmetry
The axis of symmetry is a fundamental characteristic of parabolas; it's a vertical line that divides the parabola into two mirror images. Each point on the parabola is equidistant from the axis of symmetry. This line of symmetry can be found by using the x-coordinate of the vertex (\( h \) from the vertex formula).

For a quadratic function \(f(x) = ax^2 + bx + c\), the equation of the axis of symmetry is \(x = h\). In the given example, with the vertex's x-coordinate at -0.5, the axis of symmetry is the line \(x = -0.5\). This becomes a critical aid in sketching the parabola, ensuring it is accurately represented on the graph with respect to its symmetry.
X-Intercepts
X-intercepts, also known as the roots or zeros of the function, are the points where the parabola crosses the x-axis. These points occur where the function output \(f(x)\) is zero. To find the x-intercepts algebraically, we set the quadratic equation equal to zero and solve for \(x\).

For the quadratic function \(-x^2 + x - 30\), we solve the equation \(0 = -x^2 + x - 30\) to find the intercepts. By factoring or using the quadratic formula, we determine that the intercepts are located at \(x=6\) and \(x=-5\). These intercepts are fundamental for graphing because they mark the points where the parabola touches or crosses the x-axis.
Quadratic Function Standard Form
The standard form of a quadratic function is typically expressed as \(f(x) = a(x - h)^2 + k\), where \((h,k)\) is the vertex of the parabola, and \(a\) is a coefficient that determines the direction and width of the parabola. This form makes it easy to determine the vertex and whether the parabola opens upwards or downwards (positive or negative \(a\)), and how wide or narrow it is (the magnitude of \(a\)).

For the quadratic function in the exercise, translating the given equation into standard form reveals the essential characteristics of the parabola. By completing the square or using vertex form conversion, we obtain \(f(x) = -(x + 0.5)^2 + 29.75\). This cleanly shows the vertex at \(-0.5, 29.75\) and confirms that the parabola opens downwards given the negative \(a\), which in this case is -1.

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