Thanks for the clarification denverdoc, I guess neither me nor my teacher realized that by taking the sqrt we had a +/- .5114. For my approach, and not knowing the answer that my teacher got, is there any other way to tell that I should have used the negative amplitude instead of the positive one?
I came across a physics problem for homework that I was able to work out on my own, however when I got to class, my teacher said that my numbers were not what the book had calculated, but couldn't tell if there was a flaw in my logic that would prevent me from getting the correct phi and...