just replace x^2+4 with a
factor out on left side
(x^2+4)^2+32=12(x^2+4)
replace x^2+4 with a
a^2+32=12a
minus 12a both sides
a^2-12a+32=0
solve
factor
what 2 numbers mulitply to get 32 and add to get -12
-4 and -8
(a-4)(a-8)=0
set each to zero
a-4=0
a=4
a-8=0
a=8
remember
a=x^2+4
so
4=x^2+4
0=x^2
0=x
8=x^2+4
4=x^2
+/-2=x
x=-2, 0, 2
