Question

What is the rectangular equivalence to the parametric equations?

Answer 1

Notice that

(x - 1)²/4 + (y + 2)²/9 = (2 sin(θ))²/4 + (3 cos(θ))²/9

… = sin²(θ) + cos²(θ)

… = 1

Solve for y in terms of x :

(x - 1)²/4 + (y + 2)²/9 = 1

(y + 2)²/9 = 1 - (x - 1)²/4

(y + 2)² = 9 - 9/4 (x - 1)²

y + 2 = ± √(9 - 9/4 (x - 1)²)

y + 2 = ± 3/2 √(4 - (x - 1)²)

y = -2 ± 3/2 √(4 - (x - 1)²)

In order for the square root to be defined, one needs

4 - (x - 1)² ≥ 0

(x - 1)² ≤ 4

-2 ≤ x - 1 ≤ 2

-1 ≤ x ≤ 3

so x must belong to the interval [-1, 3].