For the sequence 15, 22, 29, 36, 43, ... , solve the following problems

Question

smileyxl3 · Answer

a.	Write a recursive formula for the sequence.
b.	Write an explicit formula for the sequence.
c.	Find the sum of the first 100 terms of the sequence.

anonymous · Answer

For a.  I would say $$
a_1=15 \quad \text{and}\quad a_{n+1} = a_n +7
$$

rane · Answer

whts the rule or difference have u found out for the numbers above ? @smileyxl3

nirmalnema · Answer

a= first term of the series= 15
d = common difference=a2=a1 = 7

nirmalnema · Answer

sum of 1st hundred terms
=100/2 (2(15)+(100-1)7)
50(30+(99)7)
= 36150

smileyxl3 · Answer

@nirmalnema I get everything except why you have to multiply 2*15

hartnn · Answer

because the formula says so, 
$\Large S_n= (n/2) (\color {red}2a_1+(n-1)d)$

smileyxl3 · Answer

@hartnn I have no idea why I didn't see that in the first place. Thanks

hartnn · Answer

no problem, welcome ^_^