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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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Oksana_A [137]

Answer:

17.6 m²

Step-by-step explanation:

Given the ratio of similar shapes = a : b, then

area of shapes = a ² : b²

Δ PTQ and Δ PRS are similar and so the ratio of corresponding sides are equal, that is

PT : PR = 6 : 9 = 2 : 3, thus

ratio of areas = 2² : 3² = 4 : 9

let the area of Δ PQT be x, then using proportion

\frac{4}{x} = \frac{9}{x+22} ( cross- multiply )

9x = 4(x + 22) ← distribute

9x = 4x + 88 ( subtract 4x from both sides )

5x = 88 ( divide both sides by 5 )

x = 17.6

Thus area of Δ PQT = 17.6 m²

5 0
3 years ago
A clerk is marking up merchandise 34%. The original price of an item is $455. What will be the retail price?
Galina-37 [17]
Take the orginal price and multiply it by 1.34.
455 * 1.34 = $609.70 in retail.

The longer way would be to take 34% of 455 and then add it to 455.

4 0
4 years ago
Write the equation of a line in slope intercept form that is perpendicular to the line y = –4x and passes through the point (2,
Gnesinka [82]

1. If the line that we are searching for is perpendicular to the line y = -4x, this means that the gradient of our line and the gradient of the perpendicular line will multiply to give -1. Thus if we call the gradient of our line m, then:

m*(-4) = -1

-4m = -1

m = 1/4

2. Since we know that m = 1/4 and we have a point (2,6) on our line, we can use the formula y - y1 = m(x - x1) to find the equation of our line, where (x1, y1) is the coordinates of a point on the line. Thus:

y - y1 = m(x - x1)

y - 6 = (1/4)(x - 2)

y - 6 = (1/4)x - 2/4 (Expand (1/4)(x - 2))

y = (1/4)x - 1/2 + 6 (Simplify 2/4 and add 6 to each side)

y = (1/4)x + 11/2 (Evaluate -1/2 + 6)

Slope-intercept form is given by y = mx + c. As our equation is already in this form, there is nothing more to do. Thus, the answer is y = (1/4)x + 11/2

6 0
3 years ago
The product of a number and 8 less than the number is –15. Find the number. and plz explain
blondinia [14]

Answer:

It can be 5 or  3

Step-by-step explanation:

let x = that number

x * (x - 8) = -15

xx  - 8x + 15 = 0

xx -  3x  - 5x + 15 = 0

x(x - 3) - 5(x - 3) = 0

(x - 5)(x - 3) = 0

then x = 5 or  x = 3

4 0
3 years ago
A student drops a penny of a house that is 16 feet tall if the equation of height as a function is h(t)= -16t2 + initial height
Molodets [167]

Answer:

it will take 3.5 seconds

Step-by-step explanation:

3 0
3 years ago
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