Впрямоугольном треугольнике dce с прямым углом с проведена биссектриса ef причем fc=13 см. найдите расстояние от точки f до прямой de

расстояние от точки до прямой измеряется по перпендикуляру. проведём fm перпендикулярно de.

треугольник cef = треугольнику emf (прямоугольные, гипотенуза ef общая, угол cef = углу def, т.к ef - биссектриса). => fm = cf=13 (см)

astrakhan the city, which stands on the banks of the volga. we lived in a hotel "azimuth". a good hotel, but it is clear that it only began reshaping of the scoop to the civilized. rooms are not yet altered, so they do not look very aesthetically pleasing. but the window opens a wonderful view of the volga. the hotel has free wifi, right up to the 7th floor is not always a good thing to achieve. the hotel has a very good restaurant. also nearby there are a few not bad restaurants. probably better to go to astrakhan in the summer or spring, but there were circumstances and we were in the city in february. everyone who thinks that astrakhan - a southern city, and it's warm i can report that we were freezing in the "warm" city. despite the fact that the temperature was only -5 was very wet and windy. all roads have turned into a skating rink, and when you look around the feeling that the whole city poured water and immediately frozen. in astrakhan, if anyone knows, has a citadel of white stone. i recommend everyone to visit this place, very beautiful.

ас1/с1в=1/1, ва1/а1с=3/7, ав1/в1с=1/3,  s a1b1c1=s abc - s ac1b1 - s c1ba1 - s a1cb1, обе части уравнения делим на s abc

s a1b1c1 / s abc = 1 - (s ac1b1/s abc) - (s c1ba1/ s abc) - (s a1cb1/s abc)

s abc=1/2*ab*ac*sina, s ab1c1=1/2*ac1*ab1*sina, ab=ac1+c1b=1+1=2, ac=ab1+b1c=1+3=4, s ab1c1/s abc=(ac1*ab1)/(ab*ac)=(1*1)/(2*4)=1/8,

s  abc=1/2*ab*bc*sinb, s c1ba1=1/2*c1b*ba1*sinb, bc=ba1+a1c=3+7=10, 

s c1ba1/s abc=(c1b*ba1)/(ab*bc)=(1*3)/(2*10)=3/20, 

s abc=1/2*ac*bc*sinc, s a1cb1=1/2*a1c*b1c*sinc, s a1cb/s abc=(a1c*b1c) / (ac*bc)=(7*3)/(4*10)=21/40,

s a1b1c1/s abc=1-1/8-3/20-21/40=8/40=1/5, или s abc/s a1b1c1=5/1