Please explain too

In Exercises $2-7,$ calculate ${\displaystyle \underset{x}{\overset{\phantom{}}{}}}fds,$ where $f$ and $x$ are as indicated.

$7.f(x,y,z)=2x-y^{\frac{1}{2}}+2z^2,$

$x(t)=\{\begin{array}{ccc}(t,& t^2,0)if& 0t1\\ (1,& 1,t-1)if& 1t3\end{array}$