The switch is opened at the time t = 0, the voltage Vs at t = 0+ is:
1
\(V\left[ {\frac{{{R_1}}}{{{R_1} + {R_2}}}} \right]\)
2
\(V\left[ {\frac{{{R_2}}}{{{R_1} + {R_2}}}} \right]\)
3
\(V\left[ {\frac{{{R_1}}}{{{R_2}}}} \right]\)
4
\(V\left[ {\frac{{{R_2}}}{{{R_1}}}} \right]\)