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Find the prime factorization of each number. The factors of 72 are 3x3x2x2x2; the prime factors of 18 are 2x3x3. For each pair of factors, one of that number can move outside the radical. So
becomes 3*2
or 6
, and
becomes 3
.
Now, the square root of -18 is a complex number--I'm not sure if you've been over that, but the square root of -1 is defined to be i. So by definition,
= -1. So that makes your square root of -18 to be 3i
.
Combine your coefficients and your answer is (9-3i)(
).
