Equations – roots and powers

How many roots does x⁶ –12x⁴ + 32x² = 0 have?
(A) 1
(B) 3
(C) 4
(D) 5
(E) 2

Solution:

x^6 –12(x^4) + 32(x^2) = x^2 (x^4 – 12x^2 + 32) = x^2 (x^2 – 4)(x^2 – 8)

The roots are 0, ±2, and ±2√2: a total of 5.
Please remember that ‘0’ is also a root.
The correct answer is D