1. 9y²-6xy+x²
2. a²-6a+9-3a²+6a=9-2a²
3. a) x²-6x+9-x²-2.7x=9
-8.7x=0, x=0
b) (3y-5)(3y+5)=0
3y-5=0, 3y=5, y1=5/3=1 2/3
3y+5=0, 3y=-5, y= -1 2/3 (одна целая две третьих)
4. a) (x²+1)(x²-1)=(x^4-1)
b) (3a²-6b²)(a²+2b²)=
=3(a²-2b²)(a²+2b²)=
=3(a^4-4b^4)