x=(a^2-b^2):(a-b)^2:b

1) ( а^2 - b^2 ) : ( a - b )^2 = ( ( a - b )( a + b )) : ( ( a - b )( a - b )) = ( a + b ) / ( a - b )
2) ( a + b )/( a - b ) : b = ( a + b ) /( b( a - b )) = ( a + b ) / ( ab - b^2 )