17. (x + 1)⁴ + (x + 1)² - 6 = 0

Let y = (x+1)². Then y² + y - 6 = 0.

(y+3)(y-2) = 0

y = -3 or y = 2

(x+1)² = -3 (no real solutions) or (x+1)² = 2

x+1 = ±sqrt(2)

x = -1 ± sqrt(2)