If Dy/Dx=5, Dr/D(theta)= 18, and y=40, find theta.

[TDavenport]

Could anyone give me some advice as to how to solve this? P.S. Sorry if this should've gone in the Calculus forum, I didn't know which would be more appropriate.

 

[Simon Bridge]

Welcome to PF;
Lets see if I understand: you want to solve: $$\frac{dy}{dx}=5\; ;\; \frac{dr}{d\theta}=18$$ ... for $\theta$ ?

There is not enough information ... we need to know the relationship between x y r and $\theta$.
If you know those, then you apply the operations to the relations and use algebra.

 

[Ssnow]

I think also that there is a problem in the request, if $y=40$ how can be possible that $\frac{dy}{dx}=5$?

 

[TDavenport]

Welcome to PF;
Lets see if I understand: you want to solve: $$\frac{dy}{dx}=5\; ;\; \frac{dr}{d\theta}=18$$ ... for $\theta$ ?

There is not enough information ... we need to know the relationship between x y r and $\theta$.
If you know those, then you apply the operations to the relations and use algebra.

I didn't think there was enough information either, but this was all my professor gave me and he said it is somehow possible :(

 

[Simon Bridge]

@TDavenport: Context... what have the recent lessons been about?
Maybe something about polar coordinates?

@Ssnow: y = 5x ... dy/dx = 5 for all values of y ... but that was not the request.