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3 years ago

Derive the equation of the parabola with a focus at (-5,5) and a directix of y = -1

Mathematics

1 answer:

Paladinen [302]3 years ago

7 0

Answer:

Step-by-step explanation:

From any point (x, y) on the parabola the focus and directrix are equidistant

Using the distance formula

$\sqrt{(x+5)^2+(y-5)^2}$ = | y + 1 |

Squaring both sides

(x + 5)² + (y - 5)² = (y + 1)^2 , that is

(y + 1)² = (x + 5)² + (y - 5)² ← subtract (y - 5)² from both sides

(y + 1)² - (y - 5)² = (x + 5)² ← expand left side and simplify

y² + 2y + 1 - y² + 10y - 25 = (x + 5)²

12y - 24 = (x + 5)² ← factor left side

12(y - 2) = (x + 5)² ← divide both sides by 12

y - 2 = $\frac{1}{12}$ (x + 5)² ← add 2 to both sides

y = $\frac{1}{12}$ (x + 5)² + 2

f(x) = $\frac{1}{12}$ (x + 5)² + 2 → D

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x - 2y = 3 5x + 3y = 2 The lines whose equations are shown intersect at which point? (1, -1) (-1, 1) (0, 3/2)

gtnhenbr [62]

I would solve the first equation for x and then sub that value into x in the second equation. That's the easiest way. x - 2y = 3 solved for x is x = 2y+3. Now sub that in for x in the second equation: 5(2y+3)+3y=2 and 10y + 15 + 3y = 2. 13y = -13, and y = -1. Now sub that y value into either equation to solve for x: x = 2(-1) + 3 gives us an x value of x = 1. Therefore, your solution to this system is (1, -1), first choice above.

4 0

3 years ago

We are studying the proportion of cities that have private garbage collector. We want a maximum error of 0.10 and a 95% confiden

True [87]

Answer:

The minimum number of cities we need to contact is 96.

Step-by-step explanation:

In a sample with a number n of people surveyed with a probability of a success of $\pi$ , and a confidence interval $1-\alpha$ , we have the following confidence interval of proportions.

$\pi \pm z\sqrt{\frac{\pi(1-\pi)}{n}}$

In which

Z is the zscore that has a pvalue of $1 - \frac{\alpha}{2}$ .

The margin of error is:

$M = z\sqrt{\frac{\pi(1-\pi)}{n}}$

95% confidence interval

So $\alpha = 0.05$ , z is the value of Z that has a pvalue of $1 - \frac{0.05}{2} = 0.975$ , so $Z = 1.96$ .

In this problem, we have that:

$p = 0.5, M = 0.1$

$M = z\sqrt{\frac{\pi(1-\pi)}{n}}$

$0.1 = 1.96*\sqrt{\frac{0.5*0.5}{n}}$

$0.1\sqrt{n} = 0.98$

$\sqrt{n} = 9.8$

$(\sqrt{n})^{2} = (9.8)^{2}$

$n = 96$

The minimum number of cities we need to contact is 96.

8 0

3 years ago

A line that passes through 2 or more lines are called a?

11Alexandr11 [23.1K]

Answer:

transversal

Step-by-step explanation:

1. In geometry any line which passes through or intersects 2 or more line are called a transversal.

2.Transversal are generally used in geometry of Euclidean plane to decide whether the given set of lines through which transversal passes are parallel or not.

8 0

3 years ago

PLEASE HELP!!

PSYCHO15rus [73]

Answer:

The bird is approximately 9 ft high up in the tree

Explanation:

The required diagram is shown in the attached image

Note that the tree, the cat and the ground form a right-angled triangle

Therefore, we can apply special trigonometric functions

These functions are as follows:

$sin(\alpha)=\frac{opposite}{hypotenuse} \\ \\ cos(\alpha)=\frac{adjacent}{hypotenuse} \\ \\tan(\alpha)=\frac{opposite}{adjacent}$