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Mice21 [21]
3 years ago
15

Which is the equation of an ellipse with directrices at x = ±4 and foci at (2, 0) and (−2, 0)?

Mathematics
1 answer:
NemiM [27]3 years ago
6 0

Answer:

x squared over 4 plus y squared over 8 equals 1

Step-by-step explanation:

The general equation of ellipse is given as;

(x²/a²) + (y²/b²) = 1

The coordinates of a foci are: (±c, 0) where;

c² = b² - a²

However, we know that equation of directrix is; x = ±a/e

Now, Directrix is given ±4

Thus, a/e = 4

a = 4e

We also know that c = ae from ellipse foci coordinates.

Thus, ae = 2

since ae = 2, then (4e)e = 2

4e² = 2

e² = 2/4

e = 1/2

Thus;

a = 4 × 1/2

a = 2

Since c² = b² - a²;

2² = b² - 2²

4 = b² - 4

b² = 8

From (x²/a²) + (y²/b²) = 1, we can put our values to get;

x²/4 + y²/8 = 1

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Answer:

Scale factor of  cube to the smaller cube is 5 : 3.

Step-by-step explanation:

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Scale factor of these cubes = \sqrt[3]{\text{ratio of the volumes of the cubes}}

                                              = \sqrt[3]{\frac{\text{volume of large prism}}{\text{Volume of small prism}}}

                                              = \sqrt[3]{\frac{125}{27} }

                                              = \frac{5}{3}

                                              = 5 : 3

Therefore, scale factor of  cube to the smaller cube is 5 : 3.

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