WebWork is dumb

I'm doing my Diff Eq homework, okay? We're solving the equations representing damped oscillation of a spring-mass system. And it wants me to translate the answer from the form Asin(kt)+Bcos(kt) to Ccos(ωt-α). A pretty natural thing to do, since sums of trig functions are a pain to deal with. Once I get my answer it wants me to enter my values for C, ω, and α. My C—fine. My ω—fine. But apparently my α is totally wrong. Which is odd, because I got α from the same system of equations I got C from. So if one is right, the other should be right. I bashed myself against the WebWork forever, double and triple checking my work, but no. I was right. I called my dad in to make sure I wasn't making any dumb mistakes, which made me explain everything. There was nothing wrong with my work. So on a whim I decided to add 2π to the correct value, since this would be equivalent. And of course, it was correct. Apparently they don't like negative values of α. Stupid.

So I go on, and do a problem where I'm supposed to use variation of parameters which is really complicated but happens to work out well. I put in my answer, which includes a logarithm. This answer, the system informs me, is WRONG. It can't take the natural logarithm of a negative number. So I put an absolute value inside the log. WebWork tells me two things: 1) this answer is equivalent to the one I just submitted, and 2) this answer is correct. Stupid.