How do you simplify sqrt(-3)sqrt(-12)?

1 Answer
Oct 30, 2017

sqrt(-3)sqrt(-12) = -6

Explanation:

What is interesting about this example is that it is a counterexample to the often quoted "identity":

sqrt(a)sqrt(b) = sqrt(ab)

In fact this identity only holds if at least one of a or b is non-negative.

By convention, the principal square root of a negative number n is given by:

sqrt(n) = isqrt(-n)

So:

sqrt(-3)sqrt(-12) = i sqrt(3) * i sqrt(12) = i^2sqrt(3)sqrt(12) = -1 * sqrt(3 * 12) = -sqrt(36) = -6