15.
1)
=(х^4-1)(х^4+1)/(х^4-1)=х^4+1
16.
1)
=(2у^2-2у^2+16у)/(у-8)=
=16у/(у-8)
14.
1)
=(х-у)(б+а)/(а+б)(у-х)=-1
18.
1)
=(2-аб)/а(2+б) +2б/(2+б)=
=(2-аб+2аб)/а(2+б)=
=(2+аб)/а(2+б)
20.
2)
=(а-б)(а+б)(х-у)(х+у)/(х+у)(а-б)=
=(а+б)(х-у)
1)
=7/(х-у)(х+у) -5/х(у-х)=
=(7х+5х+5у)/х(х-у)(х+у)=
=(12х+5у)/х(х^2-у^2)
19.
2)
=14а(а-б)(а+б)/7(а-б)(а+б)^2=
=2а/(а+б)