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dix123
 one year ago
Can someone help me write an equation for a parabola using a focus and directrix? Medal and follow.
dix123
 one year ago
Can someone help me write an equation for a parabola using a focus and directrix? Medal and follow.

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welshfella
 one year ago
Best ResponseYou've already chosen the best response.2http://hotmath.com/hotmath_help/topics/findingtheequationofaparabolagivenfocusanddirectrix.html this should help

welshfella
 one year ago
Best ResponseYou've already chosen the best response.2yw a simple one worth remembering is the parabola y^2 = 4ax where the focus is at (a,0) and directrix is x = a

welshfella
 one year ago
Best ResponseYou've already chosen the best response.2dw:1436266138651:dw

welshfella
 one year ago
Best ResponseYou've already chosen the best response.2derivation: P is the point (x,y) the lines marked with 2 lines are equal (definition of a parabola) so a + x = sqrt (y^2 + (x a)^2) (a + x)^2 = y^2 + x^2  2ax + a^2 a^2 + x^2 + 2ax = y^2 + x^2  2ax + a^2 which reduces to y^2 = 4ax

welshfella
 one year ago
Best ResponseYou've already chosen the best response.2dw:1436266598022:dw

welshfella
 one year ago
Best ResponseYou've already chosen the best response.2so if you need the equation of a parabola given focus = (2,0) and directrix x = 2 we can write ir straight away a = 2 y^2 = 4(2)x y^2 = 8x
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