Salut !
en supposant que ABCD est un rectangle
angle ADE = 180° - (90° + 60°) = 30°
angle EDC = 90° - 30° = 60°
angle DEC = 180° - (60° + 40°) = 80°
angle BEC = 180° - (80° + 60°) = 40°
angle ECB = 90° - 40° = 50°
