Question

Answer 1

Tam giác ABC, có DE//BC

Theo định lí ta-lét, ta có :

\(\Rightarrow\dfrac{AD}{DB}=\dfrac{AE}{EC}\)

hay \(\dfrac{12}{18}=\dfrac{AE}{30}\)

\(\Rightarrow AE=\dfrac{30.12}{18}=20\left(cm\right)\)

Vậy AE  20 cm

Answer 2

Xét tam giác ABC: DE // BC (gt).

\(\Rightarrow\dfrac{AD}{BD}=\dfrac{AE}{CE}\left(Talet\right).\)

\(Thay:\) \(\dfrac{12}{18}=\dfrac{AE}{30}.\Rightarrow AE=20\) (đvđd).