Which equation is equivalent to
f(x) = 16x4 – 81 = 0?
(4x2 - 9)(4x2 - 9) = 0
(4x2 + 9)(4x2 - 9) = 0
(4x - 9)(4x - 9) = 0
(4x + 9)(4x - 9) = 0