121y-y^3 and y^2-11y: having trouble factoring

[g187play]

I am having trouble factoring these.

121y-y^3=(11-y)(11+y^2) ???

y^2-11y = (y+11) (y-11)

This is driving me crazzzzy! I am not sure what to do with all those "y"'s!
I can handle a y^2 - 18
y^2-81= (y+9)(y-9)

 

[Denis]

Re: 121y-y^3 and y^2-11y

Slow down :wink:

121y - y^3
= y(121 - y^2)
= y(11 + y)(11 - y)