What is the sum of sqrt(-81)√−81 and 3sqrt(-25)3√−25?

1 Answer
A. S. Adikesavan
Mar 28, 2016

-21i, -9i, 9i and 21i−21i,−9i,9iand21i or, in brief, the sum = (+-6+-15)i(±6±15)i, where i = sqrt(-1)√−1 .

Explanation:

Separately, the complex numbers are isqrt81=+-i9√81=±i9 and i3sqrt25=3(+-5)i3√25=3(±5)i.
The sum is =(+-9+-15)i=(±9±15)i.

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