Help.. Locus/focal chord (1 Viewer)

[Arkie]

hi
im having troubles with such questions suuc as

Find the equation if the line passing through P and focus F of the parabola.

(eq of the parabloa previously found being x^2 = 3y and P(-3,3) and focus already worked out to being (3/4, 0)

like
i just cant seem to work out the equation from having the focus and having a point that lies on the parabola

please help
thanks
arkie

 

[cwag]

if u have two points...u can just use the two point formula of a line.. y-y1 = m(x-x1) where m= (y2-y1)/(x2-x1)

 

[kaz1]

hi
im having troubles with such questions suuc as

Find the equation if the line passing through P and focus F of the parabola.

(eq of the parabloa previously found being x^2 = 3y and P(-3,3) and focus already worked out to being (3/4, 0)

like
i just cant seem to work out the equation from having the focus and having a point that lies on the parabola

please help
thanks
arkie

(y-y₁)/(x-x₁)=(y₂-y₁)/(x₂-x₁)

(y-3)/(x+3)=(0-3)/(0.75+3)
(y-3)/(x+3)= -4/5
5(y-3)=-4(x+3)
5y-15=-4x-12
4x+5y-3=0

 

[bored of sc]

hi
im having troubles with such questions suuc as

Find the equation if the line passing through P and focus F of the parabola.

(eq of the parabloa previously found being x^2 = 3y and P(-3,3) and focus already worked out to being (3/4, 0)

like
i just cant seem to work out the equation from having the focus and having a point that lies on the parabola

please help
thanks
arkie

As Kaz said, two point formula (see his top line of working for the formula).

 

[Arkie]

(y-y₁)/(x-x₁)=(y₂-y₁)/(x₂-x₁)

(y-3)/(x+3)=(0-3)/(0.75+3)
(y-3)/(x+3)= -4/5
5(y-3)=-4(x+3)
5y-15=-4x-12
4x+5y-3=0

ok i also got that answer
however in my text book
the answer is
3x+4y-3=0
so having that in mind
the m (the gradient) should be -3/4
and i dont understand how the piss you can get that for the gradient
is the text book wrong??
or am i not picking up on something??

 

[kaz1]

ok i also got that answer
however in my text book
the answer is
3x+4y-3=0
so having that in mind
the m (the gradient) should be -3/4
and i dont understand how the piss you can get that for the gradient
is the text book wrong??
or am i not picking up on something??

I can't see any fault in my answer. Either the textbook is wrong or I have made a mistake somewhere. Hopefully someone picks up that mistake.

 

[Arkie]

kaz ur not wrong
i made the mistake as the focus was wrong
i had the focus as being (a,0)
when it was meant to be (o.a)
so wrong information
so about that mate
so i ended up getting the right answer