What is the value of the expression √9y^4 + 12√y^6 - 3√y^6 - √y^4

3y^2 + 12y^3 - 3y^3 - y^2

combine like terms from ascending to decending, you get:

9y^3 + 2y^2

If you mean by √9y^4 √(9y^4) and so on then

√9y^4 + 12√y^6 - 3√y^6 - √y^4=3y²+12y³-3y³-y²
=2y²+9y³
√9y^4 + 12√y^6 - 3√y^6 - √y^4=y²(2+3y)

But if you mean by √9y^4 (√9y)^4 then
√9y^4 + 12√y^6 - 3√y^6 - √y^4=81y²+12y³-3y³-y²
√9y^4 + 12√y^6 - 3√y^6 - √y^4=80y²+9y³=y²(80+y)

its 12y^4-y^2+3y = y*(12y^3-y+3)=0
So y=0 and i dont know about the rest but i gave you one answer there is another two good luck with that

0