Question 191938
x^4+5x^2-36=0

usually  we  do  x^2+x-4 =0  for  example

but  just  use  same  tech

(x^2  -4) (x^2 +9)=0

use  FOIL  to  check

now  lets  look further

(x^2-4)  is  pattern  for  difference  of  squares  so

(x+2)  (x-2)  is  that  factor

unfortunately  x^2 +9  looks  factorable  but  is not

in  summary

(x+2) (x-2)  (x^2+9)  =0