1) a / ( a - b ) - ( a /( a + b )) = ( a( a + b ) - a( a - b )) / ( a² - b² ) = ( a² + ab - a² + ab ) / ( a² - b² ) = 2ab / ( a² - b² )
2) ( m + n )/ ( m - n ) * ( m - n ) / m = ( m + n ) / m
3) ( x : ( x - 3 )) : ( x² / ( 3x - 9 )) = ( x ( 3x - 9 )) / ( ( x - 3 )* x² ) = ( 3( x - 3 )) / ( x( x - 3 )) = 3 / x