Q7 Oct 2008

Someone please tell me that I've made some mistake and that f⁽⁴⁾ e^2x sin 3x is NOT..

16e^2xsin3x + 8e^2xcos3x + 8e^2xcos3x - 4e^2xsin3x + 4e^2xcos3x - 4e^2xsin3x + ... {16 terms in all}

Even in a 12-hour paper my blood would run cold if I came across something like that.

Failing an error on the 4th derivative, may I hope to have made a mistake about the method we use? (ie. maximise the xi term to give a "worst case error"

You must keep adding the terms together at the end of each derivative calculation. It helps. I ended up getting -119e^2xsin(3x) - 120e^2xcos(3x). [edit: lecturer is in agreement up to here and so my calculations further should be fine]

My end result for that question was 96 panels after some rounding and ensuring an even value.

Thanks. Yes that makes sense. I think some of the terms might even vanish. Again, I suppose if it eats time, it also spits out marks in return, so it's not really something for me to be whingeing about.