Question 29688
x^4 + 12x^2 -64 = 0
(here you must know how we make factors i.e splitting of the middle term...if you might not know then please contact me again ,,and i will explain to you)...

x^4 + (16-4)x^2 -64 = 0 ...by solving brackets..we get

x^4 +16x^2  -4x^2 -64 = 0

taking common from first two and last two variables...we get

x^2(x^2 +16)  -4 (x^2 +16)= 0 

or  (x^2-4) (x^2 +16) =0 

Here further factorization can be possible,,,

or [(x)^2 - (2)^2] (x^2 +16) =0 

now , in first variables i.e.[(x)^2 - (2)^2] ,,,,,we can apply the formula 
(a^2 - b^2)= (a+b)(a-b).....  and we get 

 [(x - 2)(x + 2}] (x^2 +16) =0 

Please feel free to revert back for any further queries.