sequence and series (1 Viewer)

[bos1234]

Find a value of n and of n and of Tn, if Tn belongs to the sequence
4,-1,-6,... and Tn< -204

 

[-pari-]

gah. i wrote out a whole reply and it disappeard.

okay anyway

arithmetic series with a= 4, d= -5
Tn= 4 -5n +5
= 9 -5n

9 - 5n < -204
5n > 213
n > 42.something (i'm guessin - dont have my calc with me)

so since its bigger than 42.something we take the next whole number
n = 43

sub this into the equation to get Tn.
Tn = 4 + (42 x -5)

press some calculator buttons and voila.

 

[bos1234]

k thanks!