What is the solution to x 4 + 4x 3 ≤ 12x 2?

Move 12x² to the left and factor: x⁴ + 4x³ − 12x² = x²(x + 6)(x − 2). Since x² is nonnegative, the product is less than or equal to zero when (x + 6)(x − 2) is nonpositive; this occurs from −6 to 2, including both endpoints. Thus the solution is [−6, 2], choice B.

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