Let $C$ be the line segment from $(0,0)$ to $(2,2)$, and let $f(x,y)=x^2+y$.

Write down a vector equation $r(t)$ of the line segment, that is, find a parametrization of $C$.

The answer given is $r(t)=\langle t,t\rangle,0\le t\le 2$.

**My Question: How did they get $\boldsymbol{r(t)=\langle t,t\rangle}$?**