$7\mathrm{.}68$ Determine $i_x(t)$ in the circuit of Fig. P$7\mathrm{.}68,$ given that $u_s(t)=6cos5{10}^{5}tV.$

Figure P$7\mathrm{.}68$: Circuit for Problem $7\mathrm{.}68.$ Solve by finding the thevenin equivalent of the diamond region.