I think I answered the second one here :
http://web2.0calc.com/questions/help_49408#r1
First one
12x^2 - 64 = -x^4 add x^4 o both sides
x^4 + 12x^2 - 64 = 0 factor as
(x^2 + 16) (x^2 - 4) = 0
(x^2 + 16) (x + 2) (x - 2) = 0
We only have 4 solutions..... setting the last two factors to 0 and solving for x we get that x = 2 and x = -2
So....the first answer is correct