Conics Help (1 Viewer)

[tacogym27101990]

hey i have what seems like a pretty easy question.
but i keep getting it wrong
and i dont understand terry lee's working out

the question is :

3x-2y-1=0 is a chord of the ellipse x^2 + 4y^2 = 9. find the co-ordinates of its midpoint

terry lee says 2y = 3x-1
so then he subs it into the ellipse but then he just says x^2 +(3x-1)^2 = 0

why!?
i did the same thing but then when i subbed it in i had x^2 +2(3x-1)^2=9

help please??

thanks in advance

 

[Mark576]

x² + 4y² = 9 (1)
2y = 3x - 1 (2)

From (2), 4y² = (3x - 1)²

Substitute this into (1):

x² + (3x - 1)² = 9 and solve from there.

 

[tacogym27101990]

thanks
that was pretty stupid of me
but does that mean theres a typo where her says x^2 + (3x - 1)^2=0??
not that it will affect the answer
but im just curious

 

[Affinity]

You don't need to solve the quadratics.. all iis asked for is the sum of the roots divded by 2

 

[tacogym27101990]

yeah i no that
thats what i did
but when he subbed in (3x-1)^2
the 9 just disappeared
why?

 

[jkwii]

cos terry lee is sometimes wrong, can't help thaqt.he's not perfect.

 

[tacogym27101990]

thort so
just making sure
thanks