WOW, okay i'm going to say all this in a very non judgemental way here.
First off why degrade YOURSELF just in order to get your child a better grade in math? Have you tried helping you herself with it, or getting her a tutor?
Honestly maybe she is just not grasping it enough and needs to just go ahead and flunk it this year and then take it again next year. I funcked algebra 2 the first year i took it because of not doing homework, i was getting good grades on tests, but simply didn't want to do the homework every day. Is this what is going on with your child?
What ever the reason for her flunking, she should either get a tutor, or else just take it over again next year. I mean come on, how would you feel if you did sleep with this man, thinking it was going to get your daughter a better grade, and then find out that he still gives her the same grade?
I think you'd feel pretty used and helpless at that point, not to mention foolish. Make your daughter earn what she gets the right way... I mean how would you feel if your daughter was to grow up and do the same thing, or worse yet... think that if she slept with the teacher..(if he was a perv) that she would get a good grade. I think if you heard she had done something like this you'd be outraged...
Think also how she would feel about you if she found out you did this just to get her a better grade, do you think she may take it as she needs to sleep with people in order to get ahead in life? I think she would and i know as a mother you wouldn't like the idea that you had put it into her head by doing this!