# plot parametric curve from symbolic expressions

I would like to get the plot of the parametric curve $(x1(t),x2(t)$ for $t$ in $[0,1]$.

var('ts')

x1sol=vector([-cos(ts),sin(ts)])*exp(ts/2)

x11 = x1sol[0]

show(plot(x11(ts),x12(ts),(ts,0,1)))

I get the error:
*TypeError: unable to simplify to float approximation*

I would like to avoid formulation as :

def x1(t): ....