# Thread: Need help with calculations on an arc I'm drawing out for a project

1. ## Need help with calculations on an arc I'm drawing out for a project

I'm in real need of some help I'm making a little project and need to plot an out an arc and don't have a giant protractor so can anyone tell me how to work out the height of line A or even give me the answer

Many thanks
David

2. ## Re: Need help with calculations on an arc I'm drawing out for a project

three graph screenshots attached ...

3. ## Re: Need help with calculations on an arc I'm drawing out for a project

Hi skeeter thanks but can you explain this as a long time since iv that to do stuff like this (Nearly 20 years lol)

4. ## Re: Need help with calculations on an arc I'm drawing out for a project

Originally Posted by Nutcase1
Hi skeeter thanks but can you explain this as a long time since iv that to do stuff like this (Nearly 20 years lol)
You are basically looking for the equation of a parabola: $(x-h)^2=4a(y-k)$.
$(h,k)$ is the vertex which is $(0,1220)$. We know that the point $(1830,~1530)$ is also on the curve.
Given all that you should be able to work out $a=~?$ BTW $a>0$.

5. ## Re: Need help with calculations on an arc I'm drawing out for a project

I used a circular arc ...