Question

giúp em phần 5.2 với ạ em   đang gấp

Answer 1

a) Sửa đề: Chứng minh \(\Delta DAB\) \(\sim\) \(\Delta CBD\)

Xét \(\Delta DAB\) và \(\Delta CBD\) có:

\(\widehat{DAB}=\widehat{CBD}\left(gt\right)\)

\(\widehat{ABD}=\widehat{BDC}\) (so le trong)

\(\Rightarrow\Delta DAB\sim\Delta CBD\left(g-g\right)\)

b) Do \(\Delta DAB\sim\Delta CBD\) (cmt)

\(\Rightarrow\dfrac{AD}{BC}=\dfrac{AB}{BD}=\dfrac{BD}{CD}\)

*) \(\dfrac{AD}{BC}=\dfrac{AB}{BD}\)

\(\Rightarrow BC=\dfrac{AD.BD}{AB}\)

\(=\dfrac{4.6}{3}=8\left(cm\right)\)

*) \(\dfrac{AB}{BD}=\dfrac{BD}{CD}\)

\(\Rightarrow CD=\dfrac{BD.BD}{AB}\)

\(=\dfrac{6.6}{3}=12\left(cm\right)\)