(х² - 2xy +y²)/(x² - xy -7x+7y) : (х²- xy +7x-7y)/(x² - 49) =
= (x-y)² / (x(x-y) +7(-x+y)) : ( х(х-у) + 7(х-у) ) / (х² - 7²) =
= (х-у)² / (х(х-у) -7(х-у)) : ( (х-у)(х+7) ) / ( (х-7)(х+7) ) =
= (х-у)² / ( (х-у)(х-7) ) : (х-у)/(х-7) =
= (х-у)/(х-7) * (х-7)/(х-у) =
= (х-у)(х-7) / (х-7)(х-у) =
= 1/1 = 1