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What is the equation of the quadratic graph with a focus of (4,3) and a directrix of y=-6

Rufina [12.5K]

Answer:

f(x) = (1/18)x^2 - (4/9)x - 65/18

Step-by-step explanation:

Since the focus (4,3) is higher up than is the directrix y = -6, the vertex is between y = -6 and y = 3, halfway between these values, to be exact: y = -3/2. Thus, the y-coordinate of the vertex is (-6 + 3/2), or -4.5. The x-coordinate of the vertex is 4, which comes from that 4 in (4,3). Thus, the vertex is (4, -4.5) or (4, -4 1/2).

The standard equation for a vertical parabola with vertex at (h,k) is:

4p(y-k) = (x-h)^2, where p is the distance between vertex and focus or between vertex and directrix. In this case p = 4.5. Thus, the equation of this quadratic is 4(4.5)(y - [-4.5]) = (x - 4)^2, or

18(y+4.5) = (x-4)^2, or y+4.5 = (1/18)(x-4)^2.

Let's expand this and rewrite the result as a quadratic equation in standard form y = ax^2 + bx + c:

y + 4.5 = (1/18)(x^2 - 8x + 16). Multiplying all terms by 18 to remove both fractions, we get:

18y + 81 = x^2 - 8x + 16. Rearranging these terms, we get:

18y = x^2 - 8x + 16 - 81, or

18y = x^2 - 8x - 65, or

y = f(x) = (1/18)x^2 - (4/9)x - 65/18.

5 0

3 years ago

Read 2 more answers

How to do a k over 8 equals 7

11Alexandr11 [23.1K]

Let's deconstruct the equation.

K x (1/8) = 7

You want to isolate K, so you multiply by 8 for both sides (since 8 x 1/8 = 1)
So, K = 7 x 8

K=56

6 0

3 years ago

What is the slope of the graph shown below?

Alecsey [184]

The slope is 4/3x.

Since the y-intercept is (0,-3), you go up and see that the next point is (1,1).

8 0

3 years ago

Don't have to do all of them just tell me the ones you do.

Alik [6]

See explanations below.

Step-by-step explanation:

12. If H(x) represent the percent of U.S households with internet use in x years after 1980 then;

a) H(23)=55 means the number of U.S households with internet use in 23 years after 1980 is 55

b)H(4)=k

so if in 23 years H, is 55, find in 1 year

In 1 year H= 55/23=k

c)H(27) ≥ 61 means in 27 years the number of U.S households with Internet use will be greater or equal to 61 households. If you check the results, in 27 years, H is 55/23 * 27 =64.5 ≅65 households which is at most 61 households.

d) H(17) + H(21)=H(29) means the sum of households with internet use in 17 years and 21 years after 1980 equal the number of households with internet use in 29 years.Checking the results;

H(17) = 55/23 *17 =40.65

H(21)=55/23 *21=50.22

H(17)+H(21)=40.65+50.22=90.87≅91 households

H(29)=55/23 * 29 = 69.34≅69 which is False

13.

h(x)=-7x ; h(x)=63 ⇒replacing x in the second function with -7x

-7x=63

x=63/-7

x=-9

14.

t(x)=3x ; t(x)=23

3x=23

x=23/3 = 7.67

14.

m(x) =4x +15 ; m(x)=7

4x+15=7

4x=7-15 -----------collecting like terms

4x=-7

x=-7/4

15.

k(x)=6x-12 ; k(x) =18

6x-12=18

6x=18+12-------collecting like terms

6x=30

x=30/6

x=5

16. q(x) =1/2x -3 , q (x) =-4

1/2 x-3 =-4------------multiply each term by 2

x-6= -8 ----------------collect like terms

x= -8+6

x= -2

17.

j(x)= -4/5 x + 7 ; j(x)= -5

-4/5 x +7 = -5 ---------multiply each term by 5

-4x+35= -25

-4x=-25-35

-4x=-60

4x=60

x=60/4

x= 15

Learn More

Functions ; brainly.com/question/2316114

Keywords : Functions

#Learnwithbrainly

3 0

3 years ago

Mr. Luis wants to sell his house. The state he lives in charges a 3.5% sales tax on the sale of a house. The county charges a 3.

GarryVolchara [31]

We have been given that Mr. Luis wants to sell his house. The state he lives in charges a 3.5% sales tax on the sale of a house. The county charges a 3.9% sales tax, and the city charges a 2.2% sales tax.

We are asked to find the total tax, if Mr Luis sells his home for $122,500.

To find total tax, we will add all tax rates as they are being applied to same base.

$\text{Total of tax rates}=3.5\%+3.9\%+2.2\%$