Help me, please

I need help with this

I guess this is  ???

[ a - b ] /  [ a + b ]    -  {2ab ]  / [ a^2 - b^2 ]

Factor the denominator of the second fraction

[ a - b ]  /  [ a + b ]  -   [ 2ab ] /  [ (a + b) ( a - b) ]

Multiply the first fraction by  [ a - b]  in the numerator and denominator

[ (a - b) (a - b)] / [ (a + b) (a - b) ]  -  [2ab ] / [ (a + b) (a - b) ]

[ (a - b) (a - b) - 2ab ] / [ (a + b) ( a - b) ]

[ a^2  - 2ab + b^2  - 2ab ] / [ (a+ b) (a - b) ]

[ a^2  - 4ab + b^2 ]  / [ a^2  - b^2 ]