Bonjour,
1) U(A) = E
U(D) = O
U(B) = (R₂ + R₃) x E/(R₁ + R₂ + R₃)
U(C) = R₃ x E/(R₁ + R₂ + R₃)
E = 5V R₁ = 2kΩ R₂ = 3kΩ et R₃ = 5kΩ
U(A) = 5 V
U(B) = 0,8 x E = 4 V
U(C) = 0,5 x E = 2,5 V
2) Re = R₃//R₄ = R₃R₄/(R₃ + R₄)
U(A) = E
U(D) = 0
U(B) = (R₂ + Re) x E/(R₁ + R₂ + Re)
U(C) = Re x E/(R₁ + R₂ + Re)
Re = (5k x20k)/(5k + 20k) = 100.10³/25 = 4 kΩ
U(B) = (3 + 4) x 5/(2 + 3 + 4) = 35/9 = 3,88 V
U(C) = 4 x 5/9 = 20/9 = 2,22 V
