(x + 1)4 - 5(x + 1)2 + 4 = 0
let (x+ 1 )2 = a---------------------(1)
a2 - 5a + 4 = 0
a2 - a - 4a + 4 = 0
a( a - 1) - 4 (a - 1) = 0
(a-1)(a- 4) = 0
a-1 = 0 or a- 4 = 0
a = 1 or a = 4
but a = ( x + 1 )2 from (1)
( x+ 1 )2 = 1 or ( x + 1 ) 2= 4
x + 1 = +1 or -1 or x + 1 = 2 or -2
x + 1 =1 or x + 1 = -1 or x + 1 = 2 or x + 1 = -2
x = 1 - 1 or x = -1 -1 or x = 2 - 1 or x = -2 -1
x = 0 or x = -2 or x = 1 or x = -3