📏Honors Pre-Calculus Unit 10 – Analytic Geometry

Key Concepts

• Analytic geometry combines algebra and geometry to analyze geometric shapes using coordinate systems
• Coordinate systems assign ordered pairs of numbers (coordinates) to points in a plane or space
• Distance formula calculates the distance between two points in a coordinate plane using their coordinates
• Midpoint formula finds the coordinates of the point halfway between two given points
• Equations of lines describe lines in a coordinate plane using slope, y-intercept, or point-slope form
  • Slope represents the steepness and direction of a line
  • Y-intercept is the point where a line crosses the y-axis
• Conic sections result from intersecting a plane with a double cone and include circles, ellipses, parabolas, and hyperbolas
• Parametric equations represent curves using separate equations for x and y coordinates in terms of a parameter (usually t)
• Polar coordinates specify points using a distance from the origin (r) and an angle from the positive x-axis (θ)

Coordinate Systems

• Cartesian coordinate system uses two perpendicular number lines (x-axis and y-axis) to assign coordinates to points in a plane
  • x-axis runs horizontally, with positive values to the right and negative values to the left of the origin
  • y-axis runs vertically, with positive values above and negative values below the origin
• Origin is the point (0, 0) where the x-axis and y-axis intersect
• Coordinates are written as (x, y), where x represents the horizontal distance and y represents the vertical distance from the origin
• Quadrants are the four regions formed by the x-axis and y-axis
  • Quadrant I: x > 0, y > 0
  • Quadrant II: x < 0, y > 0
  • Quadrant III: x < 0, y < 0
  • Quadrant IV: x > 0, y < 0
• Three-dimensional coordinate system adds a third axis (z-axis) perpendicular to both the x-axis and y-axis
• Spherical and cylindrical coordinate systems are alternative ways to represent points in three-dimensional space

Distance and Midpoint Formulas

• Distance formula: $d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$, where $(x_1, y_1)$ and $(x_2, y_2)$ are the coordinates of two points
• Distance formula is derived from the Pythagorean theorem
• Midpoint formula: $(\frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2})$, where $(x_1, y_1)$ and $(x_2, y_2)$ are the coordinates of two points
• Midpoint is the point that divides a line segment into two equal parts
• Distance and midpoint formulas can be extended to three-dimensional space by including the z-coordinates
• Applications include finding the length of a diagonal in a rectangle or the center of a circle given two points on its circumference

Equations of Lines

• Slope-intercept form: $y = mx + b$, where $m$ is the slope and $b$ is the y-intercept
• Point-slope form: $y - y_1 = m(x - x_1)$, where $(x_1, y_1)$ is a point on the line and $m$ is the slope
• Standard form: $Ax + By + C = 0$, where $A$, $B$, and $C$ are constants and $A$ and $B$ are not both zero
• Vertical lines have an undefined slope and are represented by equations of the form $x = a$, where $a$ is a constant
• Horizontal lines have a slope of zero and are represented by equations of the form $y = b$, where $b$ is a constant
• Parallel lines have the same slope but different y-intercepts
• Perpendicular lines have slopes that are negative reciprocals of each other

Conic Sections

• Circles have the general equation $(x - h)^2 + (y - k)^2 = r^2$, where $(h, k)$ is the center and $r$ is the radius
• Ellipses have the general equation $\frac{(x - h)^2}{a^2} + \frac{(y - k)^2}{b^2} = 1$, where $(h, k)$ is the center, $a$ is the horizontal semi-axis, and $b$ is the vertical semi-axis
  • Eccentricity ($e$) measures how much an ellipse deviates from a circle ($0 \leq e < 1$)
• Parabolas have the general equation $y = a(x - h)^2 + k$ (vertical) or $x = a(y - k)^2 + h$ (horizontal), where $(h, k)$ is the vertex and $a$ determines the direction and width
  • Focus and directrix are key elements in defining a parabola
• Hyperbolas have the general equation $\frac{(x - h)^2}{a^2} - \frac{(y - k)^2}{b^2} = 1$ (horizontal) or $\frac{(y - k)^2}{a^2} - \frac{(x - h)^2}{b^2} = 1$ (vertical), where $(h, k)$ is the center, $a$ is the horizontal semi-axis, and $b$ is the vertical semi-axis
  • Asymptotes are lines that a hyperbola approaches but never touches

Parametric Equations

• Parametric equations express x and y coordinates separately in terms of a parameter (usually t)
  • x = f(t) and y = g(t), where f and g are functions of t
• Parametric equations can represent curves that are not functions, such as circles or figure-eights
• To convert parametric equations to a Cartesian equation, eliminate the parameter by solving for t in one equation and substituting it into the other
• Applications include modeling projectile motion, planetary orbits, and cycloids
• Parametric equations can be used to find the tangent line to a curve at a given point

Polar Coordinates

• Polar coordinates (r, θ) specify a point's position using its distance from the origin (r) and the angle from the positive x-axis (θ)
  • r is the radial coordinate (distance) and θ is the angular coordinate (angle)
• Polar axis is the reference line from which angles are measured (usually the positive x-axis)
• Polar equations are equations written in terms of r and θ, such as r = 2sin(3θ)
• To convert between polar and Cartesian coordinates, use the formulas x = r cos(θ) and y = r sin(θ)
• Polar coordinates are useful for representing curves with symmetry around the origin, such as circles, cardioids, and rose curves
• Polar form of a complex number is z = r(cos(θ) + i sin(θ)), where r is the modulus and θ is the argument

Applications and Problem Solving

• Analytic geometry has numerous real-world applications in fields such as physics, engineering, computer graphics, and navigation
• Coordinate systems provide a framework for analyzing and solving geometric problems algebraically
• Distance and midpoint formulas are used in geometry, computer graphics, and navigation systems (GPS)
• Equations of lines are essential in linear regression, computer vision, and 3D modeling
• Conic sections describe the paths of planets and satellites, the shapes of mirrors and lenses, and the trajectories of projectiles
  • Parabolic mirrors focus light and sound waves (telescopes, microphones)
  • Elliptical orbits of planets and satellites around celestial bodies
• Parametric equations model motion and curves in physics, animation, and robotics
  • Projectile motion (cannon shots, basketball free throws)
  • Particle trajectories in fluid dynamics and electromagnetism
• Polar coordinates simplify the analysis of certain curves and are used in navigation, astronomy, and antenna design
  • Radar systems use polar coordinates to track objects
  • Planetary orbits and spiral galaxies are more easily described using polar equations
• Problem-solving strategies in analytic geometry include translating word problems into equations, visualizing problems using graphs, and applying appropriate formulas and theorems