bob

Almost for get to bob!!
well, this is a short unit, easier then other unites but also hard in some way.
I think i understand everything in 6.1 (might forget some part,but I'm try to review)
6.2 was all about accumulation function which a function in side a function. I get the idea o it, but may be not the calculation part yet. have to review that over again.
6.3 the fundamental theorem.i think i get 1/2 of it. need some more time for it too.
6.4 the area, i think I'm fine with it.
hope i can do better on this test ^_^