Question

1) Cho tu giac ABCD co AB=2,5cm; AD=4cm; BD=5cm; BC=8cm; CD=10cm. CMinh ABCD la hinh thang

3) Cho tam giac ABC co AB=4cm, D thuoc AC, AD=2cm, DC=6cm. Biet goc A=100, goc B-C=20. Tinh goc ABD