Sagot :
Soit x la largeur de la rivière
SB/(20+x) = tg20°
SB/x = tg32° --->SB = xtg32 et SB = tg20°(20+x)
donc xtg32° = tg20°(20+x) ---> xtg32° = 20tg20° + xtg20°
x(tg32° - tg20°) = 20tg20°
x = 20tg20°/(tg32°- tg20°) = 27,901
SB = xtg32° = 17,434