### Home > A2C > Chapter 9 > Lesson 9.3.2 > Problem 9-163

9-163.

For homework, Londa was asked to simplify the expression

. She got the answer 7, but when she checked, she learned that the correct answer was −7. Homework Help ✎ Show Londa the steps she could take to get −7.

What steps do you think Londa took to get 7 as a result?

What does she need to consider in order to avoid making this mistake in the future?

Londa's example means that it is not always true that

for real numbers*a*and*b*. What restriction needs to be placed on the numbers*a*and*b*?

First eliminate the negative sign from each radical by replacing it with *i*.

Remember that *i* is the square root of −1, now finish multiplying.

−7

See parts (a) and (b).

The variables *a* and *b* must be non-negative real numbers.