решите систему:
х+у=17
ху+9у-9х-81=0

 Х = 17 - Y Y*( 17 - Y) - 9Y - 9*( 17 - Y) + 81 = 0 17Y - Y^2 - 9Y - 153 + 9Y + 81 = 0 - Y^2 + 17Y - 72 = 0 ---------------------------------------D = 289 - 288 = 1 ; V D = 1 Y1 = ( - 17 + 1 ) : ( - 2 ) = + 8 Y2 = ( - 18 ) : ( - 2 ) = + 9 ------------------------------------X = 17 - Y X1 = 17 - 8 = 9 X2 = 17 - 9 = 8