$17-34.$ Scalar line integrals Evaluate the following line integrals along the curve $C.$

$17.{\displaystyle \underset{C}{\overset{\phantom{}}{}}}xyds$;$C$ is the unit circle $r(t)=($:$cost,sint$:$),$ for $0t2.$

$18.{\displaystyle \underset{c}{\overset{\phantom{}}{}}}(x^2-2y^2)$ ds; $C$ is the line segment $r(t)=($:$\frac{t}{\sqrt[\phantom{2}]{2}},\frac{t}{\sqrt[\phantom{2}]{2}}$:$),$ for $0t4.$

$19.{\displaystyle \underset{C}{\overset{\phantom{}}{}}}(2xy)ds$;$C$ is the line segment $r(t)=(3t,4t),$ for $0t2.$