Cho hinh thang co duong cao 10 cm . Hieu hai day la 22 cm . Keo dai day nho bang day lon de thanh hinh chu nhat co chieu dai bang day lon, chieu rong bang chieu cao hinh thang . Dien tich duoc mo rong them bang 1/7 dien tich hinh thang cu.Phan mo rong ve phia ben phai co dien tich 90cm vuong .Hay tinh day lon cua hinh thang ban dau

cho hinh tam giac abcd co day nho ab la 27cm , day lon cd la 48 cm neu keo dai day nho ve phia b them 5 cm thi dien tich cua hinh tang len 40 cm2.Tinh dien tich hinh thang da cho

a)Mot hinh tam giac ABC co day BC la 34,5dm. Neu keo dai canh BC ve phia C mot doan bai 7 dm thi dien tich tang them 42 dm2 .Tinh dien tich hinh tam giac ABC.

b)Mot hinh thang co tong hai day la 78dm,day lon bang 7/6 day nho .Chieu cao bang 1/2 day lon .Tinh dien ich hinh thang do

1 hinh thang co chieu cao 10m , hieu hai day la 22 m . Keo dai nho cho bang day lon thanh 1 hinh chu  nhat co chieu dai bang day lon, chieu rong bang chieu cao . Dien tich mo rong 1/7 dien tich cu. Phan mo rong ve phia tay phai co  dien tich 90 m2. Tinh day lớn của hình thang ban đầu .

tim dien tich hinh thang biet neu keo dai day be ve mot phia thi ta duoc hinh vuong co chu vi la 24m

mot dam ruong hinh thang co dien tich 1155m2 va co day be kem day lon 33m nguoi ta keo dai day be them 20m va keo dai day lon them 5m ve cung mot phia de duoc hinh thang moi dien tich hinh thang moi nay bang dien tich cua mot hinh chu nhat co chieu rong bang 30m va chieu dai 51m hay tinh day be day lon cua hinh thang ban dau

1 hinh thang co chieu cao la 10m hieu 2 day la 22m keo dai day nho = day lon de hinh da cho thanh hinh chu nhat co chieu dai = day lon chieu rong = duong cao hinh thang dien tich duoc mo rong them = 1/7 dien tich hinh thang cu 1 phan mo rong them co dien tich la 90m2 

mot thua ruong hinh thang co day be 42m day lon bang 7/3 day nho nguoi ta keo dai day len ve mot phia them 6m nen dien tich tang them 108m2 tinh dien tich thua ruong sau khi keo dai them day lon

                                    _{Mot hinh thang co chieu cao bang 10m hieu 2 day la 22m keo dai day nho bang day lon de hinh da cho thanh hinh chu nhat co chieu dai bang day lon chieu rong bang duong cao hinh thang dien tich duoc mo rong them 1/ 7 dien tich hinh thang cu phan mo rong them co dien tich la 90m2 tinh do dai day lon cua hinh thang ban dau}