Substitute a for x + 3:

Factor:

Set each factor = 0:

Substitute (x + 3) back in the expressions and solve.

x³a⁴ + 2x²a³ = 0

x²a³(ax + 2) = 0

x²a³ = 0 or ax + 2 = 0

x²(x + 3)³ = 0
x² = 0
x = 0
(x + 3)³ = 0
x = −3

ax + 2 = 0
(x + 3)x + 2 = 0
x² + 3x + 2 = 0
(x + 2)(x + 1) = 0
x = −2; x = −1