1. The problem statement, all variables and given/known data Task is to write differential equation for this circuit. E, R1, R2, R3, L are constants. 2. Relevant equations Ul = L di/dt 3. The attempt at a solution I guess, we have to use current method for each contour. 1st contour equation: E = U1 + U2 + Ul = i*(R1+R2) + L di/dt Equation arround the loop: E = i*R1 + i2*(R1+R3) It means that I got system: E=i*(R1+R2) + L di/dt +i2*R1 E = i*R1 + i2*(R1+R3) The problem is i2. I need to get i2, I guess, from second contour using L, R2 and R3. Can someone help quickly? I need this task until tomorrow. Or I have done something wrong at the begining?