Part A
First, we need to find the drone's distance from the controller, r, when θ = π/2. We'll substitute π/2 into our function r(θ).
r(π/2) = 2 + 3cos(π/2)
We know from the unit circle that cos(π/2) = 0.
r(π/2) = 2 + 3(0) = 2
So, at this instant, the drone is 2 meters from the controller.
Next, let's find the rectangular coordinates (x, y). Remember the conversion formulas from polar to rectangular coordinates: x = r cos(θ) and y = r sin(θ).
We already have r = 2 and θ = π/2.
x = 2 * cos(π/2) = 2 * 0 = 0
y = 2 * sin(π/2) = 2 * 1 = 2
The rectangular coordinates for the drone's position are (0, 2).
Part B
The drone is at the controller's position (the pole) when its distance from the origin is zero. So, we need to find where r(θ) = 0.
2 + 3cos(θ) = 0
Now, we solve for cos(θ):
3cos(θ) = -2
cos(θ) = -2/3
To find θ, we use the inverse cosine function: θ = arccos(-2/3).
Your calculator will give you the principal value, which is in Quadrant II:
θ ≈ 2.301 radians.
This is one of our answers. But here's where you need to be careful! The cosine function is also negative in Quadrant III. To find the second angle in the interval 0 ≤ θ < 2π, we can use the reference angle or the symmetry of the unit circle. The angle in Quadrant III with the same cosine value is 2π - 2.301.
θ ≈ 2π - 2.301 ≈ 6.283 - 2.301 = 3.982 radians.
So, the two values of θ are approximately 2.301 and 3.982.
Part C
To find the average rate of change of a function on an interval [a, b], we use the formula (f(b) - f(a)) / (b - a). In our case, the function is r(θ) and the interval is [0, π/2].
Average Rate of Change = (r(π/2) - r(0)) / (π/2 - 0)
We need to calculate r(0) and r(π/2).
From Part A, we know r(π/2) = 2.
Now, let's find r(0):
r(0) = 2 + 3cos(0) = 2 + 3(1) = 5
Now, plug these values into the formula:
Average Rate of Change = (2 - 5) / (π/2) = -3 / (π/2) = -3 * (2/π) = -6/π
The average rate of change is -6/π meters per radian.
Part D
We're given the rate of change function, r'(θ) = -3sin(θ). We need to determine if the drone is moving closer to or further from the controller at θ = π/3. The key here is the sign of r'(θ) at that instant.
- If
r'(θ) is positive, the distance r is increasing, so the drone is moving further away.
- If
r'(θ) is negative, the distance r is decreasing, so the drone is moving closer.
Let's evaluate r'(π/3):
r'(π/3) = -3sin(π/3)
We know that sin(π/3) = √3 / 2.
r'(π/3) = -3 * (√3 / 2) = -3√3 / 2
Since √3 is positive, r'(π/3) is a negative number.
Justification: Because r'(π/3) < 0, the rate of change of the distance from the controller is negative at this instant. Therefore, the drone is moving closer to the controller.