Ответ:

• (5х+5у) / (х²-ху)
• 15/4
• 3,75

Объяснение:

(х²-у²)/5х² : (х²-2ху+у²)/25х =

= (х²-у²)/5х² * 25х/(х²-2ху+у²) =

= (х-у)(х+у)/5х² * 25х/(х-у)² =

= ( (х-у)(х+у)*25х ) / (5х²*(х-у)²) =

= ( (х+у)*5*5х) / (5х*х*(х-у)) =

= ( (х+у)*5) / (х*(х-у)) =

= (5х+5у) / (х²-ху) =

при х=4, у=2:

= (5*4+5*2) / (4²-4*2)=

= (20+10) / (16-8) =

= 30/8 = 15/4 = 3,75