choi tam giac ABC AB<ac .Tia phan giac goc A cat canh Bc tai D ke BM va CN cho vuong goc vs ADC \(\left(CM,N\in AD\right)\)

\(tamgiacBND\approx tamgiacCND\)

\(\frac{ab}{ac}=\frac{bm}{cn}\)

\(\frac{1}{DM}-\frac{1}{DN}=\frac{2}{AB}\)

\((\frac{x^2+1}{x^2-1}-\frac{1}{x-1})(\frac{4}{x-1}-\frac{2}{x})\)