Find the standard form of the equation of the ellipse with the given characteristics.
Center: (4, 4); a = 3c; foci: (-3, 4), (11, 4)
The foci are horizontally aligned (they have the same y-coordinate), so the ellipse is horizontal.
General equation for a horizontal ellipse:
(x-h)²/a² + (y-k)²/b² = 1
with
a ≥ b
center (h,k)
vertices (h±a,k)
co-vertices (h,k±b)
foci (h±c,k), c² = a² - b²
Apply the given information and solve for h, k, a, b, and c.
(h,k) = (4,4)
h = k = 4
foci (h±c, k) = (4±7,4)
c = 7
a = 3c = 21
a² = 441
c² = a² - b²
7² = 21² - b²
b² = 21² - 7² = 392
The equation becomes
(x-4)²/441 + (y-4)²/392 = 1
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Answers & Comments
The foci are horizontally aligned (they have the same y-coordinate), so the ellipse is horizontal.
General equation for a horizontal ellipse:
(x-h)²/a² + (y-k)²/b² = 1
with
a ≥ b
center (h,k)
vertices (h±a,k)
co-vertices (h,k±b)
foci (h±c,k), c² = a² - b²
Apply the given information and solve for h, k, a, b, and c.
(h,k) = (4,4)
h = k = 4
foci (h±c, k) = (4±7,4)
c = 7
a = 3c = 21
a² = 441
c² = a² - b²
7² = 21² - b²
b² = 21² - 7² = 392
The equation becomes
(x-4)²/441 + (y-4)²/392 = 1