Question

(x+4)^4-6(x+4)^2-7=0

Answer 1

(x+4)⁴-6*(x+4)²-7=0
(x+4)²=t, t>0
t²-6t-7=0
t₁=-1,-1<0
 t₂=7
(x+4)²=7
x²+8x+16=7
x²+8x+9=0
D=28, √D=2√7
x₁,₂=(-6+-2√7)/2=-3+-√7
x₁=-3-√7
x₂=-3+√7