① ω 2 = 1/LC at LC parallel resonance, and the capacitance c =1/lω 2 =1/25 (10-3) (103) 2 = 4.

② The LC parallel resonant branch is open to the outside, and the circuit is a pure resistance circuit. Total current I = IR =120/100 =1.2a, voltage across R2 U = 1.2× 50 = 60V, inductance current IL = U/ω L = 60/(65438.