7
4,4*(7,6-2,4)*(7,6+2,4)/[2,2*(6,3-3,7)*(6,3+3,7)]=2*5,2*10/(2,6*10)=2*2=4
8
(a+b)^4=(a+b)²*(a+b²)=(a²+2ab+b²)(a²+2ab+b²)=
=a^4+2a³b+a²b²+2a³b+4a²b²+2ab³+a²b²+2ab³+b^4=
=a^4+4a²b+6a²b²+4ab³+b^4
9
x+5y=4⇒x=4-5y
4*(0,2x-y)/[5(0,2x-y)(0,2x+y)]=4/[5(0,2x+y)=4/[5*(0,8-y+y)=4/4=1