gia su co them 9cm2 thi tong dien h tang them la: 93+9=102 (cm2)
2 lan chieu rong ban dau la:102:3=34(cm)
chieu rong ban dau la: 34:2=17 (cm)
cheu dai ban dau la: 17x3=51 (cm)
dien h ban dau la: 51x17=867(cm2)
ban k va kb voi mk nha mk chac chan cau nay den 100% day