A²-2ab+b²-49/a-b-7= 9x²-6xy+y²/15x²-5xy= x+y+x²-y²/x-y+x²-2xy+y²=

1) (а²-2ab+b²-49)/(а-b-7)=(а-в)²-49  /  (а-b-7)=(а-в-7)(а-в+7)/(а-b-7)=а-b+7
2) (9x²-6xy+y²)/(15x²-5xy)=(3х-у)²/5х(3х-у)=(3х-у)/5х
3) (x+y+x²-y²)/(x-y+x²-2xy+y²)=( (х+у)+(х-у)(х+у) ) / ( х-у+(х-у)²)=
(х+у)(1+х-у)/(х-у)(1+х-у)=(х+у)/(х-у)