4.
а)=6(25-9х^2у^2)=150-54х^2у^2
б)=25а^2+30а+9+25а^2-9=
=50а^2+30а
в)=х^8-4х^4у^5+4у^10-4у^10=
=х^8-4х^4у^5
5.
1)
25у^2=4
у^2=4/25
у1=2/5
у2=-2/5
2)
4(х-2)^2+5(х-4)^2=(3х-8)^2
4(х^2-4х+4)+5(х^2-8х+16)=
=9х^2-48х+64
4х^2-16х+16+5х^2-40х+80=
=9х^2-48х+64
9х^2-56х+96=9х^2-48х+64
9х^2-56х-9х^2+48х=64-96
-8х=-32
х=4