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emmainna [20.7K]
3 years ago
11

A parabola has its focus at (1,2) and its directrix is y=-2. the equation of this parabola could be

Mathematics
1 answer:
Oksi-84 [34.3K]3 years ago
4 0
<span>x^2/8 - x/4 + 1/8 = 0 A parabola is defined as the set of all points such that each point has the same distance from the focus and the directrix. Also the parabola's equation will be a quadratic equation of the form ax^2 + bx + c. So if we can determine 3 points on the parabola, we can use those points to calculate the desired equation. First, let's draw the shortest possible line from the focus to the directrix. The midpoint of that line will be a point on the desired parabola. Since the slope of the directrix is 0, the line will have the equation of x=1. This line segment will be from (1,2) to (1,-2) and the midpoint will be ((1+1)/2, (2 + -2)/2) = (2/2, 0/2) = (1,0). Now for the 2nd point, let's draw a line that's parallel to the directrix and passing through the focus. The equation of that line will be y=2. Any point on that line will have a distance of 4 from the directrix. So let's give it an x-coordinate value of (1+4) = 5. So another point for the parabola is (5,2). And finally, if we subtract 4 instead of adding 4 to the x coordinate, we can get a third point of 1-4 = -3. So that 3rd point is (-3,2). So we now have 3 points on the parabola. They are (1,0), (5,2), and (-3,2). Let's create some equations of the form ax^2 + bx + c = y and then substitute the known values into those equations. SO ax^2 + bx + c = y (1) a*1^2 + b*1 + c = 0 (2) a*5^2 + b*5 + c = 2 (3) a*(-3)^2 + b*(-3) + c = 2 Let's do the multiplication for those expressions. So (4) a + b + c = 0 (5) 25a + 5b + c = 2 (6) 9a - 3b + c = 2 Equations (5) and (6) above look interesting. Let's subtract (6) from (5). So 25a + 5b + c = 2 - 9a - 3b + c = 2 = 16a + 8b = 0 Now let's express a in terms of b. 16a + 8b = 0 16a = -8b a = -8b/16 (7) a = -b/2 Now let's substitute the value (-b/2) for a in expression (4) above. So a + b + c = 0 -b/2 + b + c = 0 And solve for c -b/2 + b + c = 0 b/2 + c = 0 (8) c = -b/2 So we know that a = -b/2 and c = -b/2. Let's substitute those values for a and c in equation (5) above and solve for b. 25a + 5b + c = 2 25(-b/2) + 5b - b/2 = 2 -25b/2 + 5b - b/2 = 2 2(-25b/2 + 5b - b/2) = 2*2 -25b + 10b - b = 4 -16b = 4 b = -4/16 b = -1/4 So we now know that b = -1/4. Using equations (7) and (8) above, let's calculate a and c. a = -b/2 = -(-1/4)/2 = 1/4 * 1/2 = 1/8 c = -b/2 = -(-1/4)/2 = 1/4 * 1/2 = 1/8 So both a and c are 1/8. So the equation for the parabola is x^2/8 - x/4 + 1/8 = 0 Let's test to make sure it works. First, let's use an x of 1. x^2/8 - x/4 + 1/8 = y 1^2/8 - 1/4 + 1/8 = y 1/8 - 1/4 + 1/8 = y 1/8 - 2/8 + 1/8 = y 0 = y And we get 0 as expected. Let's try x = 2 x^2/8 - x/4 + 1/8 = y 2^2/8 - 2/4 + 1/8 = y 4/8 - 1/2 + 1/8 = y 4/8 - 1/2 + 1/8 = y 1/2 - 1/2 + 1/8 = y 1/8 = y. Let's test if (2,1/8) is the same distance from both the focus and the directrix. The distance from the directrix is 1/8 - (-2) = 1/8 + 2 = 1/8 + 16/8 = 17/8 The distance from the focus is d = sqrt((2-1)^2 + (1/8-2)^2) d = sqrt(1^2 + -15/8^2) d = sqrt(1 + 225/64) d = sqrt(289/64) d = 17/8 And the distances match again. So we do have the correct equation of: x^2/8 - x/4 + 1/8 = 0</span>
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ruslelena [56]
Hello!

Divide the amount of chairs (30) that 12 people can build by the number of hours (8) it takes to build them, to find out how many chairs they make per hour.

30 ÷ 8 = 3.75

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3.75 × 100 = 375

ANSWER:

The people can build D. 375 chairs in 100 hours.
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A CD has a 5% chance of being a smash hit and profiting $5.2 million, a 50% chance of being a modest success and profiting $0.9
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find the average rate of change from t=2 to t=5 for the velocity function v(t)=t^2-t+10. WILL GIVE THE BRAINLIEST ANSWER--EXPLAI
Elina [12.6K]
Answer: The average rate of change is 6.
First, plug in each value of <em>t</em> into the function, v(t) to find there coordinate pairs.

v(2) = (2)^2 - (2) + 10
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v(5) = (5)^2 - (5) + 10
v(5) = 25 + 5
v(5) = 30

You can write these values as coordinate pairs, like so: (2, 12) and (5, 30).
The formula for the average rate of change is A(x) =  \frac{f(x)-(f(a)}{x-a}. When you plug in the values from this particular case, the average rate of change formula becomes A(t) = \frac{30-12}{5-2}, or A(t)= \frac{18}{3}.

Looking at the equation, you can solve for the average rate of change between t = 2 and t = 5, which equals 6.
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3 years ago
Robert is writing a paper for language arts class. He can write 2/3 of a page in 1/4 of an hour. At what rate is Robert writing?
VLD [36.1K]

He can write 2/3 of a page in 1/4 of an hour.

=> He can write 2/3 × 4 = 8/3 = 2 and 2/3 of a page in an hour

Answer: 2 and 2/3 of a page per hour

ok done. Thank to me :>

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2 years ago
Is X-1 a factor of x^5-1?
Musya8 [376]

Answer: No

Explanation:

According to factor theorem, if f(x)=0 then x is a factor of the given function or equation.

As x-1 is a factor

We equate x-1=0

x=1

Substituting in x^5-1, we have 1^5-1 =1-1=0.

Hence, it's a factor.

When coming to x^5+1, it would become 1^5+1=1+1=2

So x-1 isn't a factor of x^5+1.

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