Locus Question Help (1 Viewer)

[Redyapper]

Hi,

The question I'm not sure how to work out is:
Find the equation of the parabola with co-ordinates of vertex (0,0), and equation of axis x=0, passing through (-1, 7).
The answer is x^2=1/7y

I think I'd use the x^2=4ay general equation, but not sure how to work out what a is...

Thanks!

 

[qrpw]

No need to work out a. Since the vertex is the origin, it has to be y = bx^2 where b is a constant. Sub (-1, 7) into it to find b, which gives 7.

 

[Timothy6340]

yea since it goes through the P(-1,7) u can just sub that into to the genral equation of x^2=4ay where u get a to be 1/28 just sub that in and u get x^2=1/7y

 

[Redyapper]

No need to work out a. Since the vertex is the origin, it has to be y = bx^2 where b is a constant. Sub (-1, 7) into it to find b, which gives 7.

how do I then get the answer of x^2=1/7y?

 

[Redyapper]

yea since it goes through the P(-1,7) u can just sub that into to the genral equation of x^2=4ay where u get a to be 1/28 just sub that in and u get x^2=1/7y

ohhhh I see. Thank you!