1. The problem statement, all variables and given/known data In the network of sinusoidal current , R2 = 10 ohm , X2 = -30*sqrt(3) ohm. Find the resistance R1 so that voltage U2 is in phase delay behind voltage U for angle alpha = - pi / 6. 2. Relevant equations 3. The attempt at a solution Z2 = sqrt(R^2 + X2^2) = 20*sqrt(7) ohms fi2 = arctg(X2/R2) = -79. 107 degrees fi = 30 + fi2 = -49.107 degrees the rest is in the picture below. The problem is that this last equation can only give complex solutions and R1 should be in real domain.