1)28-7yˇ2 = 7(4-yˇ2)=7.(2+y)(2-y)
-11xˇ2+22x-11=-11(xˇ2-2x+1)=-11.(x-1)(x-1)
xˇ3y+8y = y.(xˇ3+8)=y.(x+2)(xˇ2-2x+2)
(yˇ2-1)ˇ2-9 = (yˇ2-1+3)(yˇ2-1-3)=(yˇ2+2)(yˇ2-4)=(yˇ2+2)(y+2)(y-2)
2)3xˇ3-27x = 0
3x.(xˇ2-9)=0
3x(x+3)(x-3)=0
x=0, x=-3, x=3
3)cˇ2 +6c-40= (c-4)(c+10)