I'm sorry It's happened to me loads of times. I was supposed to tape Marion at Eastbourne when she finally got onto Centre Court (against Henin) but I completely forgot. She only got 4 games so I guess it wouldn't have mattered. During the French Open 2006 my dad taped over Safina v Sharapova because he thought Djokovic v Nadal would be better, I was really mad.
And yeah I hate maths too, I have so failed it this year.