Question

I need to find S25 for -7+-2+3+8+...

Answer 1

@eric_d

Answer 2

So you have a difference of 5.

\(\large\color{darkblue}{ \rm (-7) +5(25-1)=a_{25}}\)

Answer 3

Can you find the \(\large\color{darkblue}{ \rm a_{25} ~}\) ?

Answer 4

-7+5(24)=a25
-2(24)=a25?

Answer 5

-48=a25?

Answer 6

your second step is incorrect.

Answer 7

\(\large\color{darkblue}{ \rm (-7) +5(25-1)=a_{25}}\)
\(\large\color{darkblue}{ \rm (-7) +5(24)=a_{25}}\)
\(\large\color{darkblue}{ \rm (-7) +120 =a_{25}}\)
\(\large\color{darkblue}{ \rm 113 =a_{25}}\)