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anonymous
 one year ago
HELP PLEASE ON PRECALC, Here's the question, help quickly and correctly and you shall receive a medal! lol:
Find the standard form of the equation of the parabola with a vertex at the origin and a focus at (0, 7).
anonymous
 one year ago
HELP PLEASE ON PRECALC, Here's the question, help quickly and correctly and you shall receive a medal! lol: Find the standard form of the equation of the parabola with a vertex at the origin and a focus at (0, 7).

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anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Please help, I need to know how to do this, I am working alone online  my teacher won't help and the lesson doesn't make sense. Please help.

phi
 one year ago
Best ResponseYou've already chosen the best response.1First, plot the focus and vertex (roughly , need not be a work of art) can you do that?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0actually no, can you? not sure where everything goes

phi
 one year ago
Best ResponseYou've already chosen the best response.1vertex is (0,0) and focus is (0,7) can you plot these points?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0yepdw:1437595113760:dw

phi
 one year ago
Best ResponseYou've already chosen the best response.1and the parabola is a U shape the "curls around" the focus the vertex is the "tip" of the parabola. so it looks like this dw:1437595121260:dw

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0ok so how do we get the equation now?

phi
 one year ago
Best ResponseYou've already chosen the best response.1the standard equation for the simplest parabola (with vertex at 0,0) is y= x^2 this one is upside down, so expect it to be y =  a x^2 to find y, we use the idea that 4 p y = x^2 is the equation of a parabola and "p" is the distance from the vertex to the focus

phi
 one year ago
Best ResponseYou've already chosen the best response.1in this case, the distance from 7 to 0 is 7 (ignoring the sign) 4p is 4*7= 28 so 28y= x^2 y = 1/28 x^2 but it has to be negative because we are upside down so \[ y =  \frac{1}{28} x^2\]

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0so for p i do this: \[\left 7  0 \right = 7 so p = 7\]

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0oh ok. thanks can you help with one more. same type of problem, different info given

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Here it is: Find the standard form of the equation of the parabola with a focus at (7, 0) and a directrix at x = 7.

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0i am going to draw it is that ok?

phi
 one year ago
Best ResponseYou've already chosen the best response.1yes, just to get an idea of what is going on.

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0dw:1437595918471:dw it looks bad but i think that is the right idea?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0so what equation do i use for horizontal parabolas

phi
 one year ago
Best ResponseYou've already chosen the best response.1ok, except the vertex is exactly halfway between the directrix and focus

phi
 one year ago
Best ResponseYou've already chosen the best response.1you can just average the x values (7+7)/2 = 0 the vertex is at (0,0) this one is sideways, so swap x and y in the standard 4py= x^2 to get 4p x = y^2 just like before p is the distance from the vertex to the focus

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0which is 7 right? so p =7

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0which simplifies to 28x = y^2, but that's not an answer choice. do you want to see them?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0y = (1/28)x^2 x = (1/28)y^2 28y = x^2 y^2 = 14x

phi
 one year ago
Best ResponseYou've already chosen the best response.128x = y^2 divide both sides by 28

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0oh ok awesome! thanks so much!
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