USE SUMMATION NOTATION TO WRITE A ARITHMETIC SERIES FOR THESE TERMS. PLEASE SHOW HOW TO DO IT.

15+25+35+...; N=7
4+8+12+...; N=4
3+7+11+...;N=8

1 answer

I will do the first one.

look at 15, 25, 35, ..
there is an increase of 10 from one term to the next
so the formula will be (10n +/- something)

so if n= 1, most sigma notations start with n=1,
our first term is 10(1) + ?
what do I have to add to make the first term 15?
Isn't it 5?
so we have the expression (10n + 5)

test it: do I get 35 when n = 3 ?? YEAAH