- #1

skrat

- 748

- 8

## Homework Statement

Calculate the tangent vector to a curve $$r=R(1-\varepsilon \sin ^2 \varphi)$$ as a function of ##\varphi##

## Homework Equations

## The Attempt at a Solution

Ok, I tried like this:

I defined a vector $$(f(\varphi),\varphi)=(R(1-\varepsilon \sin ^2 \varphi),\varphi)$$ and than I calculated the derivative $$\frac{\partial }{\partial \varphi}$$ therefore my result is $$(-\varepsilon R \sin(2\varphi),1).$$

But I have a friend claiming that the result is $$(-\varepsilon R \sin(2\varphi),R(1-\varepsilon \sin ^2 \varphi)).$$ So, my question to you is... which is right? :/