# Parabola Finding the focus

• January 24th 2010, 04:39 PM
markwjak
Parabola Finding the focus
write the standard form of the equation
x^2-4x+8y+12=0
find the focus

i have it down to (x-2)^2=-8(y-8) is this right?
i'm not sure if you have to multiply the -8 on the right side of the equations by 4 since the focus is 1/4a
• January 24th 2010, 05:22 PM
skeeter
Quote:

Originally Posted by markwjak
write the standard form of the equation
x^2-4x+8y+12=0
find the focus

i have it down to (x-2)^2=-8(y-8) is this right?
i'm not sure if you have to multiply the -8 on the right side of the equations by 4 since the focus is 1/4a

$x^2-4x+4=-8y-8$

$(x-2)^2 = -8(y+1)$
• January 24th 2010, 05:27 PM
markwjak
Quote:

Originally Posted by skeeter
$x^2-4x+4=-8y-8$

$(x-2)^2 = -8(y+1)$

so how would you find the focus of the equation now -8=4a so a=-2 ?
• January 25th 2010, 03:58 AM
HallsofIvy
Quote:

Originally Posted by markwjak
so how would you find the focus of the equation now -8=4a so a=-2 ?

Yes, but a= 2 is not the focus. The focus is a point, not a number.