ouch, i guess they should post my previous post in the silly mistakes thread or make another thread called the silly idiotic mistakes.
Ok,
1.
"= 5Ck(5)^(5-k).(2/x)^k
= 5Ck(whatever)x^(k-1) "
that bit...i dunno, that was juz dumb of me.
2.
"Thirdly in your expression...