Vo=(Vm/pi)(1+cos(α))=54.02(1.707)=92.21v
Io=Vo/R=4.611a
Irms=(Vm/R)((1/2)-(α/2pi)+((sin(2α))/4pi))^0.5
=(169.7/20)((1/2)-(.785/2pi)+(sin(1.571))/4pi)^0.5
=(8.485)(.6142)
=5.21A
P=(Irms^2)*R
P=542.9w

α=45deg=.7854rad

ok what did i forget to do here

 

You haven't calculated the RMS values correctly. See the attachment for the calculation of the RMS voltage across the 20Ω resistor, and the RMS current through that resistor.

I haven't taken into account the on voltage across the SCRs which would cause the power to be a little less.

 

thank you... which computer program is that?

 

It's Mathematica. There are numerous other programs that can do that sort of thing, such as Matlab, Mathcad, Maple, Scilab, etc.