Math Problem Statement

ketch the curve represented by the parametric equations, drawing arrows to indicate the direction of increasing t. x = 3 cos(𝜃) and y = 2 sin(𝜃) with − 𝜋 2 ≤ 𝜃 ≤ 𝜋 WebAssign Plot WebAssign Plot WebAssign Plot WebAssign Plot Changed: Your submitted answer was incorrect. Your current answer has not been submitted. Eliminate the parameter to determine the Cartesian (rectangular) equation of the curve.

Incorrect: Your answer is incorrect. , x ≥ 0 or y ≥ 0

Solution

The given parametric equations are:

x=3cos(θ)andy=2sin(θ)x = 3 \cos(\theta) \quad \text{and} \quad y = 2 \sin(\theta) with the parameter range: π2θπ2-\frac{\pi}{2} \leq \theta \leq \frac{\pi}{2}

Step 1: Eliminate the parameter to find the Cartesian equation.

To eliminate θ\theta, we can use trigonometric identities. Since x=3cos(θ)x = 3 \cos(\theta) and y=2sin(θ)y = 2 \sin(\theta), let's express cos(θ)\cos(\theta) and sin(θ)\sin(\theta) in terms of xx and yy:

cos(θ)=x3andsin(θ)=y2\cos(\theta) = \frac{x}{3} \quad \text{and} \quad \sin(\theta) = \frac{y}{2}

Now, use the Pythagorean identity: cos2(θ)+sin2(θ)=1\cos^2(\theta) + \sin^2(\theta) = 1

Substitute cos(θ)\cos(\theta) and sin(θ)\sin(\theta) in this identity: (x3)2+(y2)2=1\left(\frac{x}{3}\right)^2 + \left(\frac{y}{2}\right)^2 = 1

Simplifying: x29+y24=1\frac{x^2}{9} + \frac{y^2}{4} = 1

This is the equation of an ellipse with semi-major axis 3 along the xx-axis and semi-minor axis 2 along the yy-axis.

Step 2: Determine the direction of increasing θ\theta.

For θ=π2\theta = -\frac{\pi}{2} to θ=π2\theta = \frac{\pi}{2}:

  • At θ=π2\theta = -\frac{\pi}{2}, x=0x = 0 and y=2y = -2 (bottom of the ellipse).
  • At θ=0\theta = 0, x=3x = 3 and y=0y = 0 (rightmost point of the ellipse).
  • At θ=π2\theta = \frac{\pi}{2}, x=0x = 0 and y=2y = 2 (top of the ellipse).

So, the curve starts at the bottom of the ellipse, moves to the right, and then reaches the top. The direction is counterclockwise.

Step 3: Draw the curve.

The curve is an ellipse with axes of 3 and 2, centered at the origin. You should draw arrows in the counterclockwise direction to indicate increasing θ\theta.

Step 4: Determine restrictions on xx and yy.

Given that θ\theta lies between π2-\frac{\pi}{2} and π2\frac{\pi}{2}, the cosine function (which defines xx) is non-negative, meaning x0x \geq 0. However, yy can take both positive and negative values because the sine function ranges from 1-1 to 11.

Thus, the region for the curve is restricted to x0x \geq 0, but yy can be either positive or negative.


Would you like more details on any of these steps, or have any other questions?

Here are 5 related questions for further practice:

  1. How do you parametrize an ellipse with different center points?
  2. What is the effect of changing the range of θ\theta on the parametric curve?
  3. How do you graph parametric equations using a calculator?
  4. What is the physical meaning of parametric curves in motion modeling?
  5. How do you calculate the arc length of a parametric curve?

Tip: Always check the range of your parameter carefully, as it affects the portion of the curve you are plotting!

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Math Problem Analysis

Mathematical Concepts

Parametric Equations
Cartesian Equations
Ellipses

Formulas

x = 3 cos(𝜃), y = 2 sin(𝜃)
(x/3)^2 + (y/2)^2 = 1 (Equation of an Ellipse)

Theorems

Pythagorean Identity: cos²(𝜃) + sin²(𝜃) = 1

Suitable Grade Level

Grades 10-12