# Thread: Show that at verticle turning point sign(d2x/dy2)=sign(d2x/dytheta2)

1. ## Show that at verticle turning point sign(d2x/dy2)=sign(d2x/dytheta2)

Question is on an assignment for polar curves. I am sure that at vertical turning point dx/dtheta=0 will be used. I'm not sure what sign means, could we just presume its a coefficient? It's definitely not sin.
So far I have tried d2x/dy2=d/dy(dx/dy)=d/dy(dx/dtheta*dtheta/dy) but I don't know how to go from there.
Any help appreciated.

2. ## Re: Show that at verticle turning point sign(d2x/dy2)=sign(d2x/dytheta2)

Usually, sign(x) gives you whether it is positive or negative. For example, sign(3) = 1, sign(-2) = -1. The question seems to ask you to show that the two derivative are either both positive or both negative. I hope it makes sense.

3. ## Re: Show that at verticle turning point sign(d2x/dy2)=sign(d2x/dytheta2)

Ah thanks, my tutor spent ages derping around with it and I wasn't paying attention I remember he had some moment when he realized he was making it much harder than it needed to be. Think he had forgotten the sign part.