193k views
0 votes
Find an equation for the ellipse described: Foci at (-2, 2) and (-8, 2) and vertex at (-9, 2).

a) (x+9)²/49 + (y-2)²/4 = 1
b) (x-9)²/49 + (y-2)²/4 = 1
c) (x+9)²/25 + (y-2)²/16 = 1
d) (x-9)²/25 + (y-2)²/16 = 1

1 Answer

4 votes

Final answer:

The equation of the ellipse with foci at (-2, 2) and (-8, 2) and a vertex at (-9, 2) is (x+5)^2/49 + (y-2)^2/40 = 1, but this does not match the given options, suggesting an error in the question or answer choices.

Step-by-step explanation:

To find the correct equation for the ellipse with foci at (-2, 2) and (-8, 2) and a vertex at (-9, 2), we first need to determine the lengths of the major and minor axes. The distance between the foci, which are points inside the ellipse, is 6 units (|(-2) - (-8)|). The vertex at (-9, 2) tells us that the length of the semimajor axis (a) is 1 unit larger than the distance from the center to the nearest focus since the center of the ellipse must be midway between the foci, which is at (-5, 2). Therefore, the semimajor axis is half the distance of the major axis, so it's 7 (the distance from the center to the vertex), and the major axis is 2a, which is 14. The semiminor axis (b) can be calculated using the relationship c^2 = a^2 - b^2, where c is the distance from the center to a focus. Thus, b^2 = a^2 - c^2 = 49 - 9 = 40, and b = √40. However, since we are looking for an equation of an ellipse in the form (x-h)^2/a^2 + (y-k)^2/b^2 = 1, we keep b^2 as 40. The center of the ellipse is (-5, 2), and the equation with 'a' and 'b' squared, respectively, plugged in becomes:

(x+5)^2/49 + (y-2)^2/40 = 1

This equation does not match any of the options provided, indicating a possible mistake in the question or the answer choices.

User SirSaleh
by
6.5k points