(4x-9y)/(2√x -3√y) -√y ; x+y =7.
A =(4x-9y)/(2√x -3√y) -√y = ( (2√x)² -(3√y)²) / (2√x -3√y) -√y =
(2√x -3√y)(2√x +3√y) /(2√x -3√y) -√y = || 2√x ≠3√y || = √ 2√x +3√y -√y =2(√x +√y ) .
Преобразуем x+y =7 ⇔(√x+√y )² =7 +2√(xy) ⇒√x+√y =√(7+2√(xy)).
A = 2√(7+2√(xy)).
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{x+y =72 ;√x ≠3√y.⇒x≠63/13 .y ≠28/13