What are the solutions of the equation x to the 4th power minus 5 x squared minus 36 is equal to 0 ? Use factoring to solve.

Treat x² as a single variable: x⁴ − 5x² − 36 factors as (x² − 9)(x² + 4), or (x − 3)(x + 3)(x² + 4). Setting each factor equal to zero gives x = ±3 and x² = −4, so x = ±2i. The solutions are plus or minus 3 and plus or minus 2i, which is choice C.

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