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Mathematics 20 Online
OpenStudy (anonymous):

this is for my virtual school class. I've gone through the lesson numerous times but im still struggling, any help? Derive the equation of the parabola with a focus at (0, 1) and a directrix of y = −1. A.) f(x) = −one twenty-fourth (x − 1)2 − 5 B.) f(x) = one twenty-fourth (x − 1)2 − 5 C.) f(x) = −one twenty-fourth (x + 5)2 + 1 D.) f(x) = one twenty-fourth (x + 5)2 + 1

jimthompson5910 (jim_thompson5910):

what is the vertical distance from the focus to the directrix?

jimthompson5910 (jim_thompson5910):

btw none of these answer choices work, so there is a typo somewhere

OpenStudy (anonymous):

i copy and pasted the answers but you never know i guess

jimthompson5910 (jim_thompson5910):

well the issue is that the vertex is at (0,0) but none of the answer choices have a vertex of (0,0)

jimthompson5910 (jim_thompson5910):

A and B have a vertex of (1,-5) C and D have a vertex of (-5, 1)

OpenStudy (anonymous):

whoops those were the wrong answers

OpenStudy (anonymous):

sorry

OpenStudy (anonymous):

a f(x) = −one fourth x2 b f(x) = one fourth x2 c f(x) = −4x2 d f(x) = 4x2 these are the right ones

jimthompson5910 (jim_thompson5910):

ah, much better

jimthompson5910 (jim_thompson5910):

are you able to find the vertical distance from the focus to the directrix?

OpenStudy (anonymous):

i personally cant no

jimthompson5910 (jim_thompson5910):

it might help to plot the two

jimthompson5910 (jim_thompson5910):

here's a blank xy axis |dw:1421891964960:dw|

jimthompson5910 (jim_thompson5910):

there is the focus (0,1) |dw:1421891979693:dw|

jimthompson5910 (jim_thompson5910):

now I'm adding the directrix y = -1 shown as this horizontal dashed line |dw:1421892004691:dw|

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