Question

Cho AD = 8,5cm, DB = 7cm, AE = 5,1cm, EC = x.
tính EC
 

Answer 1

Xét ΔABC có DE//BC

nên AE/x=AD/DB

=>5.1/x=8.5/7

hay x=4,2(cm)

Answer 2

Ta có:\(DE\perp AC,BC\perp AC\Rightarrow\) DE//BC

Áp dụng định lý Ta-lét ta có:

\(\dfrac{AD}{DB}=\dfrac{AE}{EC}\\ \Rightarrow\dfrac{8,5}{7}=\dfrac{5,1}{x}\\ \Rightarrow x=4,2\left(cm\right)\)

Answer 3

 X = 4,2 (cm)