(1) Why do you think we need both rectangular and polar forms?
(2) There still seems to be some confusion about the relationship between R, Xc, OR XI and the phase angle. Take a value for R and a value for XC that is ten times smaller than R and find theta, and values will do. Now solve for theta when R and Xc are equal. Finally, make Xc ten times larger than R and find theta. Do the same with R and XL.