

Cho tam giac ABC co AB=10cm, AC=15cm,AD la phan giac cua goc A
a. Biet BD=6cm. Tinh do dai CD
b. Tren duong thang AD, ta lay diem E sao cho goc ADE bang goc ACB. Chung minh tam giac CDA dong dang tam giac EDB
c. Chung minh AD.AD=AB.AC - AD.DE
a. Biet BD=6cm. Tinh do dai CD
b. Tren duong thang AD, ta lay diem E sao cho goc ADE bang goc ACB. Chung minh tam giac CDA dong dang tam giac EDB
c. Chung minh AD.AD=AB.AC - AD.DE