TITLE: How to find the LCM of One Negative and one positive Integer
QUESTION [9 upvotes]: The title pretty much explains my question. While studying theory of numbers I came across this problem. The way I did LCM in childhood gave me a negative result.Maybe the method I used is wrong.
But according to the book,
LCM(-8,20)= 40
If I use the formula LCM(a,b)= |a.b|/GCD(a,b), Then I get the right answer. But this involves finding out gcd first. Is there a direct way to solve this problem?
Thank you in advance.

REPLY [4 votes]: It is defined that: the least common multiple of two integers a and b, usually denoted by LCM(a, b), is the smallest POSITIVE integer that is divisible by both a and b. So the result must always be positive. 
Direct way to solve :Ignore the negative signs. Calculate as if everything's positive.
Hope I answered your question :)