I was wondering if there is anyone out there who
can help me solve the equasion below for 'a'.   I have
tried, and I must admit that my math skills are very
lacking.  I don't know how to work my way around the
sine of 'a', and solve for 'a'.  Any suggestions or
comments would be helpful.   BTW, this equasion will
be used to derive conduction angle from RMS and
intensity.

a = conduction angle
Vo = RMS Volts
I = Relative Intensity
Vs = RMS Supply Voltage
Pi = Pie (3.14)

                                                                        ( PI - a
 + .5 sin 2a )^1/2
Vo = Vs  ( ------------------ )
         (         PI         )