simple square root question not so simple?

Question

(4 - square root of -81) + (-9 + square root of -49) 

This is what i did as step two: 

(4 - 9i) + (-9 - 7i)
4 - 9i -9 -7i = -5 - 16i

that wasnt right so i tried simplifying the 9 in the square root of -81 to 3..

4 - 3i - 9 - 7i = -5 - 10i

neither were right.

please give me the answer.

Anonymous · Accepted Answer

-5-2i

Aaron · Answer

(4 - sqrt -81) + (-9 + sqrt -49)

This is (4 - 9i) + (-9 + 7i). That boils down to (-5 - 2i) provided they only want one answer. Whenever you take a square root, there are both positive and negative roots, even when imaginary. Really this would have 4 solutions. Along with the one I've done for you, there's the solutions to (4 + 9i) + (-9 + 7i), (4 + 9i) + (-9 - 7i) and (4 - 9i) + (-9 - 7i) if they don't want just the simplest answer.

Mark S, JPAA · Answer

You were almost right; in your first try, the problem is that it should have been (-9 **+** 7i), not **-**.

So the answer is (4 - 9i) + (-9 + 7i) or -5 -2i

Shirley · Answer

(4 - 9i) + (-9 - 7i) should be (4 - 9i) + (-9 + 7i)

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simple square root question not so simple?

4 Answers