Найдите значение выражения (а^2-2*аb/b^2 +1) : (1/а - 1/b)^2

[latex]\frac{ 3^{2} -2*3* \frac{2,1}{7} }{( \frac{2,1}{7} ) ^{2} +1}: ( \frac{1}{3} - \frac{7}{2,1} )^{2} = \frac{7*(9*7-6*2,1)}{4,41+49} :( \frac{7-70}{21} )^2= \frac{7*(63-12,6)}{53,41} :( \frac{-63}{21}) ^2= \\ =\frac{7*50,4}{53,41} :(-3)^2= \frac{352,8}{53,41}* \frac{1}{9} = \frac{39,2}{53,41}= \frac{3920}{5341}= \frac{80}{109} [/latex]

((a²-2ab)/b² +1²):(1/a-1/b)²= (a²-2ab+b²)/b² : ((b-a)²/a²b²)= (a²-2ab+b²)a²b²/ b²(b-a)²=    =(a²-2ab+b²)a²/(b²-2ab+b²)=a²    при а=3 получаем 3²=9