$\; Goi\;M ,N\;lan \; luot\;la \;giao \; cua\; DC\;voi \; AB,\;BI \;voi \;AC. \;Ta \; co:\;\frac{\overline{MB}}{\overline{MA}}= \frac{\overline{BD}}{\overline{AC}}=\frac{\overline{BA}}{\overline{AC}} ,\; \frac{\overline{NA}}{\overline{NC}}=\frac{\overline{AB}}{\overline{CA}}\rightarrow \frac{\overline{MA}}{\overline{MB}}.\frac{\overline{NA}}{\overline{NC}}=(\frac{\overline{AB}}{\overline{AC}})^2.\; Lai\;co \;AC^2=CH.BC,AB^2=BH.BC\rightarrow (\frac{AC}{AB} )^2=\frac{-\overline{HC}}{\overline{HB}}\rightarrow \;\frac{\overline{MA}}{\overline{MB}}.\frac{\overline{NA}}{\overline{NC}}.\frac{\overline{HC}}{\overline{HB}}=-1\rightarrow AH,BD,CI \; dong\; qui\;(dpcm) \; \; \; \; \;$
Bài viết đã được chỉnh sửa nội dung bởi ngoctruong236: 04-10-2013 - 19:47