# Parametric Equations

#### Prerequisite Knowledge

Coordinate Geometry and Graph Sketching: A basic understanding of the (x, y) plane, coordinates, and how to plot and interpret points.

Functions: Understanding what a function is and how it can be represented graphically.

Graph Sketching: Being able to sketch basic functions like linear, quadratic, cubic, and trigonometric functions.

Transformations of Functions: Recognizing shifts, stretches, and reflections and applying these transformations to graphs.

Trigonometry: Understanding basic trigonometric functions and their shapes can be helpful since many parametric curves utilize trigonometric functions.

Algebraic Manipulation: The ability to rearrange equations, factorize, expand brackets, and simplify expressions.

Trigonometric Identities: Recognizing and using basic trigonometric identities, such as:

•sin2x + cos2x = 1

•Double angle formulas, etc.

#### Success Criteria

1. Introduction to Parametric Equations:

Understand what a parametric representation of a curve is.

Know how to convert between parametric and Cartesian representations.

2. Sketching Parametric Curves:

Use the parameter interval to determine the portion of the curve to sketch.

Identify and plot specific points, especially when the parameter t represents time, to provide a sense of the curve’s direction.

Recognize and sketch standard parametric curves.

3. Eliminating the Parameter:

Eliminate t to derive the Cartesian equation of the curve from its parametric equations.

Use trigonometric identities, algebraic manipulations, or other methods as appropriate to eliminate the parameter.

4. Applications and Modelling:

Understand the utility of parametric equations in real-world contexts, such as physics problems involving projectile motion where parametric equations can naturally represent horizontal and vertical positions as functions of time.

#### Key Concepts

1. Introduction to Parametric Equations:

Definition of Parametric Equations: Understanding that parametric equations express each of x and y in terms of a third parameter, often t.

Advantages of Parametric Representation: Recognizing scenarios where parametric equations might be more useful or intuitive than Cartesian equations.

Parameter Range: Grasping the role of the parameter’s range in defining the part of the curve that is represented.

2. Sketching Parametric Curves:

Plotting Points: Using various values of t to obtain coordinates (x, y) for plotting.

Curve Direction: Understanding the curve’s direction by considering the parameter, especially when it represents time.

Recognizing Standard Curves: Being able to identify and sketch common parametrically defined curves, especially those based on trigonometric functions.

Interpreting Parameter Range: Recognizing how variations in the parameter range affect the portion of the curve that is drawn.

3. Eliminating the Parameter:

Conversion to Cartesian Form: Employing algebraic or trigonometric manipulations to eliminate the parameter and obtain an equation in x and y only.

Utilizing Trigonometric Identities: Using identities, such as the Pythagorean identity or double-angle formulas, to eliminate the parameter, especially in trigonometric contexts.

4. Applications and Modeling:

Real-world Context: Translating real-world scenarios into parametric representations, understanding the relevance and advantages of doing so.

Problem-solving with Parametrics: Applying parametric equations to solve problems, particularly those where the parameter has a tangible interpretation (like time in projectile motion).

Kinematics and Parametrics: In physics contexts, understanding how to represent motion, especially two-dimensional motion, using parametric equations.

#### Common Misconceptions

1. Introduction to Parametric Equations:

Equating Parameters to Cartesian: Some students might mistakenly think that the parameter t is equivalent to x or y when it’s actually a separate entity.

Parameter Utility: Students might wonder why we need parametric equations when we already have Cartesian equations, not recognizing the unique scenarios where parametrics can be advantageous.

2. Sketching Parametric Curves:

Curve Direction: Without considering the evolution of t, students might not grasp the curve’s direction, especially for loops or curves that double back on themselves.

Continuous vs. Discrete: Some may assume parametric curves are always continuous, not considering cases where the parameter might be defined for discrete values.

Standard Curves: Without ample practice, students might struggle to recognize and sketch standard parametric curves, especially those based on trigonometric functions.

3. Eliminating the Parameter:

Direct Substitution: Students might try to directly substitute t values to eliminate the parameter without proper manipulation, leading to confusion.

Over-reliance on Trig Identities: In their eagerness to eliminate the parameter, students might over-complicate equations by trying to fit them to known trigonometric identities when simpler methods are available.

4. Applications and Modelling:

Over-simplification: When translating real-world scenarios into mathematical models, students might oversimplify the situation, missing key aspects that should be modelled parametrically.

2D vs. 3D: In mechanics, when using time as a parameter, students might not differentiate between two-dimensional and three-dimensional motion, assuming parametric equations are always limited to 2D scenarios.

Parameter Interpretation: Especially in applications like mechanics, students might forget the tangible interpretation of the parameter (often time) and treat it just like any algebraic variable, losing the connection to real-world motion.

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