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Mathematics 8 Online
OpenStudy (anonymous):

=

OpenStudy (anonymous):

\(y-k)^2=4p(x-h)\) has vertex \((h,k)\) is a start

OpenStudy (anonymous):

so (2, 6)?

OpenStudy (anonymous):

close

OpenStudy (anonymous):

since you have \(-4(x+2)\) it should be \((-2,6)\)

OpenStudy (anonymous):

focus is -1?

OpenStudy (anonymous):

the next thing we need to do is find what this looks like since the \(y\) term is squared it opens left or right, not up or down and since you have a \(-4\) in front of the \(x+2\) term it opens to the left |dw:1380120974603:dw|

OpenStudy (anonymous):

since \(p=4p=-4\) you know \(p=-1\) therefore the focus is one unit TO THE LEFT of the vertex that is why we needed the vertex first

OpenStudy (anonymous):

notice that the focus is a coordinate (ordered pair) not a number, so i makes no sense to say that the focus is \(-1\) what is one unit to the left of \((-2,6)\)?

OpenStudy (anonymous):

(-1, 6)..?

OpenStudy (anonymous):

no, that is one unit to the right

OpenStudy (anonymous):

thats left on x axis?

OpenStudy (anonymous):

yes, but it is to the right of \((-2,6)\)

OpenStudy (anonymous):

start at \((-2,6)\) and go one unit to the left

OpenStudy (anonymous):

or -3 im dumb

OpenStudy (anonymous):

so (-3,6), makes the directrix 1?

OpenStudy (anonymous):

no you are not dumb, and yes, it is \((-3,6)\)

OpenStudy (anonymous):

now the directrix is a vertical line, so it looks like \(x=number\)

OpenStudy (anonymous):

since the focus is one unit to the left, the directrix is one unit to the right of the vertex what is one unit to the right of \((-2,6)\)?

OpenStudy (anonymous):

(-1), but isnt the directrix negative p, if p is -1 it should be 1?

OpenStudy (anonymous):

don't fret about the signs, they tell you which way it is open, up down or right left

OpenStudy (anonymous):

one unit to the left is because \(p\) is negative one unit to the right now for the directrix

OpenStudy (anonymous):

so just find the coordinate one unit to the right of \((-2,6)\)

OpenStudy (anonymous):

(-1,6)

OpenStudy (anonymous):

correct?

OpenStudy (anonymous):

yes, but don't forget the directrix is a line (unlike the focus, which is a point) so you want to write \(x=-1\) for the directrix

OpenStudy (anonymous):

im confused because i thought it was -p, so shouldnt it be 1?

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