Borek Mentor Messages 29,213 Reaction score 4,643 Sep 18, 2010 #2 https://www.physicsforums.com/showthread.php?t=420347
awkward Messages 364 Reaction score 0 Sep 18, 2010 #4 You can also find an extensive discussion here: http://mathforum.org/dr.math/faq/faq.negxneg.html