1) а ^ - 2 - b ^ - 2 = ( 1/a^2 ) - ( 1/b^2 ) = ( b^2 - a^2 ) / a^2b^2
2) ( ( b - a )/( ab ) )^- 2 = ( a^2b^2 ) / ( b - a )^2
3) ( b^2 - a^2 )/( a^2b^2 )•( a^2b^2 )/( b - a )^2 = ( ( b - a )( b + a ))/ ( b - a )^2 = ( b + a )/( b - a )
Ответ ( b + a ) / ( b - a )