Solved on Feb 06, 2024

Find the focus of the ellipse with equation (x+4)216+(y3)220=1\frac{(x+4)^{2}}{16}+\frac{(y-3)^{2}}{20}=1.

STEP 1

Assumptions
1. The given equation is of an ellipse in standard form.
2. The standard form of an ellipse with horizontal major axis is (xh)2a2+(yk)2b2=1\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1, where (h,k)(h,k) is the center of the ellipse, aa is the semi-major axis, and bb is the semi-minor axis.
3. The standard form of an ellipse with vertical major axis is (xh)2b2+(yk)2a2=1\frac{(x-h)^2}{b^2} + \frac{(y-k)^2}{a^2} = 1, where (h,k)(h,k) is the center of the ellipse, aa is the semi-major axis, and bb is the semi-minor axis.
4. The foci of an ellipse are located along the major axis, at a distance of cc from the center, where c2=a2b2c^2 = a^2 - b^2.
5. We are to calculate one of the foci of the given ellipse.

STEP 2

Identify the center (h,k)(h,k), the values of a2a^2 and b2b^2, and determine which axis is the major axis by comparing a2a^2 and b2b^2.
Given equation: (x+4)216+(y3)220=1 \text{Given equation: } \frac{(x+4)^{2}}{16}+\frac{(y-3)^{2}}{20}=1
Comparing with standard form: {h=4k=3a2=20b2=16 \text{Comparing with standard form: } \begin{cases} h = -4 \\ k = 3 \\ a^2 = 20 \\ b^2 = 16 \end{cases}

STEP 3

Determine which axis is the major axis by comparing a2a^2 and b2b^2.
Since a2=20a^2 = 20 and b2=16b^2 = 16, and a2>b2a^2 > b^2, the major axis is vertical.

STEP 4

Calculate the distance cc from the center to the foci using the relationship c2=a2b2c^2 = a^2 - b^2.
c2=a2b2 c^2 = a^2 - b^2
c2=2016 c^2 = 20 - 16

STEP 5

Calculate the value of cc.
c2=4 c^2 = 4
c=4 c = \sqrt{4}
c=2 c = 2

STEP 6

Since the major axis is vertical, the foci are located at (h,k±c)(h, k \pm c).
Foci: (h,k±c) \text{Foci: } (h, k \pm c)
Foci: (4,3±2) \text{Foci: } (-4, 3 \pm 2)

STEP 7

Write the coordinates of the two foci.
Focus 1: (4,3+2)=(4,5) \text{Focus 1: } (-4, 3 + 2) = (-4, 5)
Focus 2: (4,32)=(4,1) \text{Focus 2: } (-4, 3 - 2) = (-4, 1)
You can choose either focus as the solution. For instance, one of the foci of the ellipse is (4,5)(-4, 5).

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