SABD = SACD = 1/2 SABC = 300cm2 ; SABE = 1/3 SABC = 200cm2
SABD = SABM + SMBD = 300cm2 (1)
SABE = SABM + SAME = 200cm2 (2)
Lấy (1) – (2) ta được: SMBD - SAME = 100cm2
SMBD = SAME + 100
Mà: SMBD = SMCD = ½ SMBC
Mặt khác: SACD = SAME + SEMC + SMCD ; SEMC = 2 SAME
Hay SACD = SAME + 2 SAME + SAME + 100
SACD = 4 SAME +100 = 300
4 SAME = 200
SAME= 50 (cm2)