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Let \(p\) be a real number. (a) Show that the endpoints of the latus rectum of the parabola with equation \(y^{2}=4 p x\) are \((p,-2 p)\) and \((p, 2 p)\) (b) Show that the endpoints of the latus rectum of the parabola with equation \(x^{2}=4 p y\) are \((-2 p, p)\) and \((2 p, p)\)

Short Answer

Expert verified
Question: Show that the endpoints of the latus rectum of the parabolas (a) \(y^2 = 4px\) and (b) \(x^2 = 4py\) are (a) \((p, -2p)\) and \((p, 2p)\) and (b) \((-2p, p)\) and \((2p, p)\). Answer: Using the properties of parabolas and the definition of the latus rectum, we have shown that the endpoints of the latus rectum for the parabola \(y^2 = 4px\) are indeed \((p, -2p)\) and \((p, 2p)\), and for the parabola \(x^2 = 4py\) are \((-2p, p)\) and \((2p, p)\).

Step by step solution

01

Identify the focus and vertex

For a parabola with the equation \(y^2 = 4px\), the form of the parabola is vertical with its vertex at the origin (0,0). The value of \(p\) will help us find the focus. The focus of the parabola is located at \((p, 0)\). ###Step 2: Equation of the latus rectum###
02

Equation of the latus rectum

The latus rectum is a segment that is parallel to the directrix and passes through the focus of the parabola. Since the focus is at \((p, 0)\), the endpoints of the latus rectum will have the same x-coordinate, that is, x = p. ###Step 3: Find the endpoints of the latus rectum###
03

Find the endpoints of the latus rectum

We know that both endpoints of the latus rectum have an x-coordinate equal to \(p\). We need to find the corresponding y-coordinates, and we can do this by plugging x = \(p\) into the equation of the parabola, \(y^2 = 4px\). Now solve for \(y\): \(y^2 = 4p \cdot p\), \(y^2 = 4p^2\). Taking the square root of both sides, we get \(y = \pm 2p\). Therefore, the endpoints of the latus rectum are \((p, -2p)\) and \((p, 2p)\). ##Part (b)## ###Step 1: Identify the focus and vertex###
04

Identify the focus and vertex

For a parabola with the equation \(x^2 = 4py\), the form of the parabola is horizontal with its vertex at the origin (0,0). Again, the value of \(p\) will help us find the focus. The focus of the parabola is located at \((0, p)\). ###Step 2: Equation of the latus rectum###
05

Equation of the latus rectum

The latus rectum is a segment that is parallel to the directrix and passes through the focus of the parabola. Since the focus is at \((0, p)\), the endpoints of the latus rectum will have the same y-coordinate, that is, y = p. ###Step 3: Find the endpoints of the latus rectum###
06

Find the endpoints of the latus rectum

We know that both endpoints of the latus rectum have a y-coordinate equal to \(p\). We need to find the corresponding x-coordinates, and we can do this by plugging y = \(p\) into the equation of the parabola, \(x^2 = 4py\). Now solve for \(x\): \(x^2 = 4p \cdot p\), \(x^2 = 4p^2\). Taking the square root of both sides, we get \(x = \pm 2p\). Therefore, the endpoints of the latus rectum are \((-2p, p)\) and \((2p, p)\).

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Key Concepts

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

Parabola Focus and Directrix
Understanding the relationship between a parabola's focus and directrix is key to mastering the concept of conic sections. A parabola is one of the simplest forms of conic sections and is the set of all points in a plane that are equidistant from a fixed point, called the focus, and a line, known as the directrix.

The focus lies on the inside curve of the parabola, and the directrix is a line perpendicular to the axis of symmetry of the parabola, which doesn't intersect the curve. The general equation for a parabola can be expressed as either \(y^2 = 4px\) for a vertical parabola or \(x^2 = 4py\) for a horizontal parabola, where \(p\) is the distance from the vertex to the focus and directrix.

When you are given an equation of a parabola, finding the focus and directrix helps you to visualize the shape and position of the parabola in a plane. It also plays a crucial role when determining the latus rectum, as this line segment goes through the focus and has its endpoints on the parabola itself, further revealing the symmetry and geometric properties of the curve.
Quadratic Equations Graphing
Graphing quadratic equations is a fundamental skill in understanding the properties of parabolas and their appearances on a coordinate plane. A quadratic equation takes the standard form \(ax^2 + bx + c = 0\), and its graph is always a parabola. When graphing, the first step is to find the vertex of the parabola, which is the highest or lowest point on the graph, depending on whether the parabola opens upward or downward.

The axis of symmetry can be found using the formula \(x = -\frac{b}{2a}\), which gives a vertical line that divides the parabola into two mirror images. The intersection of this axis of symmetry with the parabola is the vertex. Once you have the vertex, you can plot additional points and use the reflection property to sketch the parabola.

If the parabola's equation is in \(y^2\) or \(x^2\) form, it indicates a vertical or horizontal orientation, respectively. These special forms make it easier to identify the focus and directrix, and thus the latus rectum, enabling you to graph the parabola quickly and accurately. The point where the parabola intersects its axis of symmetry is the vertex, and this point is vital for graphing the latus rectum accurately.
Conic Sections
Conic sections are the curves obtained when a cone is sliced by a plane at different angles. They include ellipses, parabolas, hyperbolas, and circles. Each conic section has unique properties and equations that describe its shape.

Parabolas are conic sections created when the cutting plane is parallel to the slope of the cone. The intersections of the plane with the cone form a symmetrical open curve. Parabolas have different orientations and can open up, down, left, or right, depending on the equation and coefficient signs. The parabola's characteristic U-shape has many practical applications, including satellite dishes and the design of car headlights, due to its reflective property that directs all incoming parallel rays through its focus.

Learning about conic sections also involves studying the relationship between the coefficients of the quadratic equation and the properties of the corresponding graph. Each parabola's focus and directrix can be determined from the equation, which, in turn, can be used to graph the quadratic function and provides insights into the conic's other characteristics, such as the latus rectum.

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