What is the simplest form of this expression?
y^2(-4y^2-7)-2y^4

First, apply the y^2 to everything in the parenthesis. This should give you:
-4y^4 -7y^2-2y^4
Next, combine any like terms.
-6y^4-7y^2
You can pull out a -y^2 from the equation.
This results in:
-y^2(6^2 +7)

Now you are done!