The complex number -5i has the complex trigonometric form of 5(cos 270o + isin 270o)

The modulus of −5i is 5, and its point lies on the negative imaginary axis, which has an angle of 270° (measured counterclockwise from the positive real axis). Thus its trigonometric form is 5(cos 270° + i sin 270°), so the statement is true.

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