Chapter 10: Problem 39
Find an equation in \(x\) and \(y\) that has the same graph as the polar equation. Use it to help sketch the graph In an \(r \theta\) -plane. $$r\left(\sin \theta+r \cos ^{2} \theta\right)=1$$
Short Answer
Expert verified
The equivalent rectangular equation is \( y + x^2 = 1 \).
Step by step solution
01
Rewrite the Polar Equation
Start with the given polar equation \( r\left(\sin \theta + r\cos^2 \theta\right) = 1 \). Distribute \( r \) to get \( r\sin \theta + r^2\cos^2 \theta = 1 \).
02
Apply Polar to Rectangular Conversion
Use the polar to rectangular coordinate conversions: \( x = r\cos\theta \), \( y = r\sin\theta \), and \( r^2 = x^2 + y^2 \). Substitute these into the equation.Since \( r\sin \theta = y \), the equation is then \( y + r^2\cos^2 \theta = 1 \). Also, since \( r^2 = x^2 + y^2 \), we have \( \cos^2 \theta = x^2/r^2 \). Use \( \cos^2\theta = (x^2)/(x^2 + y^2) \).
03
Substitute and Simplify
Substitute \( \cos^2 \theta \) in the expression:\[y + (x^2 + y^2)\left(\frac{x^2}{x^2 + y^2}\right) = 1\]yieelding:\[y + x^2 = 1\].
04
Solve the Rectangular Equation
The equation \( y + x^2 = 1 \) is a parabola that opens downwards with vertex at \( (0, 1) \). This is the rectangular equation equivalent of the given polar form.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polar Coordinates
Polar Coordinates describe a point in a plane using a distance and an angle. The distance, denoted by \(r\), represents how far the point is from the origin, while the angle \(\theta\) is measured from the positive x-axis. This system is especially useful in scenarios where symmetry and angles are more descriptive. For example a circular track or a spiral staircase.
Understanding polar coordinates requires recognizing their unique way of defining position. Unlike the more familiar Cartesian system, polar coordinates succinctly capture direction and magnitude:
Understanding polar coordinates requires recognizing their unique way of defining position. Unlike the more familiar Cartesian system, polar coordinates succinctly capture direction and magnitude:
- \(r\) is the distance from the origin to the point, which can be positive (above the x-axis) or negative (below the x-axis).
- \(\theta\) is the angle, typically measured in radians, moving counter-clockwise from the positive x-axis.
Rectangular Coordinates
Rectangular Coordinates, also known as Cartesian coordinates, provide a straightforward way of locating points using two numbers \(x\) and \(y\). Here, each coordinate denotes a point's horizontal and vertical distance from the origin in a "rectangular" fashion:
- \(x\) defines the position along the horizontal axis.
- \(y\) defines the position along the vertical axis.
Conic Sections
Conic Sections stem from the intersection of a plane with a cone. These intersections create curves known as ellipses, parabolas, and hyperbolas. These shapes are prevalent in various fields like physics, astronomy, and engineering:
- **Ellipses** have closed, oval shapes that appear in planetary orbits.
- **Parabolas** are open curves seen in satellite dishes and projectile paths.
- **Hyperbolas** have two separate branches, resembling the shape of a diverging lens.
Parabola Equation
The Parabola Equation is pivotal when discussing paths that follow a symmetrical curve. It is commonly represented as \(y = ax^2 + bx + c\):
Understanding parabolas serves as a bridge across various scientific disciplines. Their properties are crucial in architecture for designing arches, or physics for analyzing free-fall trajectories. With a profound visual impact, parabolas illustrate fundamental quadratic relationships in the natural world.
- **\(a\)** determines the direction (upwards or downwards) and width of the opening.
- **\(b\)** and **\(c\)** provide shifts and translations of the curve in the plane.
Understanding parabolas serves as a bridge across various scientific disciplines. Their properties are crucial in architecture for designing arches, or physics for analyzing free-fall trajectories. With a profound visual impact, parabolas illustrate fundamental quadratic relationships in the natural world.