Ok so we still on ch 13. This chapter is kinda sorta easy for right now because we basically use the same formulas which are arithmetic and geometric. Im going to explain the formulas for series.
Arithmetic series: Sn=(n(t1+tn))/2
Geometric series: Sn=(t1(1-r^n))/1-r
Ex: Find the sum of the first 25 terms of the series...11+14+17+20+...
first you find tn which is t25 and use the arithmetic formula which is t1+(n-1)d so it will be 11+(24)(3)=83.
Then you plug in the arithmetic series formula: Sn=25(11+83)/2=1175 and that is your answer.
The only thing i have problems with is what do i do with n when they dont tell me how many terms there are?
Subscribe to:
Post Comments (Atom)
i think what your talking about is when they ask
ReplyDeleteEX: how many multiples of 5 are between 3 and 204?
-you have to generate your own sequence using multiples of 5.
i.e. 5,10,15,....,200
I always just count them out so i don't have to memorize a formula (sorry b-rob).
I just find it easier.
if the place number isnt asked for then that probably isnt what you are looking for
ReplyDeletereview what each variable represents
tn= an actual number
n= the "address" of a number
dont get that confused
so if a problem doesnt specify an "n" essentially you are looking for a simple formula to figure out what the Tn would be for a specific address of a series
basically youre using the formuala you have memorized to make up a formula to find the tn for any address of that specific equation
1. Rule #1
ReplyDelete3n^3 + 5n^2 + 6n^4/2n^3 + 5n^4 = 6/5
2. Rule #2
lim cos (1/n)
n (infinity)
cos(1/100) = .99995
cos(1/1000) = 1
cos(1/10000) = 1
= 1