a) Có $\triangle ADE \sim \triangle CEG (g.g)$$\Rightarrow \frac{AE}{EC}=\frac{ED}{EG} (1)$Mặt khác $\triangle ABC$ có $DE//AB \Rightarrow \frac{AE}{EC}=\frac{AD}{DB} (2)$$(1)(2)\Rightarrow \frac{ED}{EG}=\frac{AD}{DB} \Rightarrow DA.EG=DB.DE$
a) Có $\triangle ADE \sim \triangle CEG (g.g)$$\Rightarrow \frac{AE}{EC}=\frac{ED}{EG} (1)$Mặt khác $\triangle ABC có DE//AB \Rightarrow \frac{AE}{EC}=\frac{AD}{DB} (2)$$\Rightarrow DA.EG=DB.DE$
a) Có $\triangle ADE \sim \triangle CEG (g.g)$$\Rightarrow \frac{AE}{EC}=\frac{ED}{EG} (1)$Mặt khác $\triangle ABC
$ có
$DE//AB \Rightarrow \frac{AE}{EC}=\frac{AD}{DB} (2)$$
(1)(2)\Rightarrow
\frac{ED}{EG}=\frac{AD}{DB} \Rightarrow DA.EG=DB.DE$