x = 2y+7 / 9y-5
9xy-5x = 2y+7
9xy-2y = 5x+7
y(9x-2) = 5x+7
y = 5x+7 / 9x-2
therefore, f-1(x) = 5x+7 / 9x-2
f(f-1(x)) = 2(5x+7/9x-2)+7 / 9(5x+7/9x-2)-5
= 10x+14+63x-14 / 45+63-45x+10
= 73x/73 = x Therefore it checks out as the inverse
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