V''=kV
V=(c1+t*c2)e^(t*√k)
令t=0,得：c1=V0
V'=V0*√k*e^(t*√k)+c2*e^(t*√k)+t*c2*√k*e^(t*√k)
令t=0,得：a0=kx0=V0*√k+c2
c2=kx0-V0√k
V(t)=[v0+t*(kx0-V0√k)]e^(t*√k)