Question

 Cho ΔABC cóMN//BC và \(\dfrac{AM}{AB}\) =\(\dfrac{1}{2}\);MN=3cm. Tính BC

 

Answer 1

Xét tam giác ABC có: MN//BC

=>\(\dfrac{AM}{AB}=\dfrac{MN}{BC}< =>\dfrac{1}{2}=\dfrac{3}{BC}=>BC=6cm\)

Answer 2

Theo định lí Ta-let, ta có: MN//BC \(\Rightarrow\dfrac{AM}{AB}=\dfrac{AN}{AC}=\dfrac{MN}{BC}=\dfrac{1}{2}\Rightarrow BC=2MN=2.3=6cm\)