if i know the reactive power KVAR and the apparent power KVA how do i work out the true power?

 

S - apparent power [VA]
Q - reactive power [VAR]
P - real power (true power) [W]
S=√(P^2+Q^2)
http://en.wikipedia.org/wiki/File:DiagramaPotenciasWPde.jpg
http://en.wikipedia.org/wiki/Pythagorean_theorem