Answer:
±90
Explanation:
√(-225) · √(-36) = (15i)·(6i) = 90i² = 90·(-1) = -90
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On the other hand, ...
... √(-225) · √(-36) = √((-225)·(-36)) = √8100 = 90
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If you consider all the roots at each stage, the result is ±90. Since you're working with complex numbers here, it is reasonable to recognize every number has two square roots.
... √(-225) = ±15i
... √(-36) = ±6i
... √(-225) · √(-36) = (±15i)·(±6i) = ±90i² = ±90