Question

find the sum of the first 25 terms of an ap whose into term is given by tn = 7-3n

Answer 1

hello users .....

we have given that :

$A_{n} = 7 - 3n$

we have to find :
sum of its 25 terms  =? 

we know that :
[tex] S_{n} = \frac{n}{2} [ a + A_{n} ] [/tex]

Here,
$a_{1} = 7 - 3*1= 7 - 3 = 4$
and
$a_{25} = 7 - 3 * 25 = 7 - 75 = - 68$

now;
sum of 25 terms :
 $S_{25} = \frac{25}{2} [ 4 + (-68) ]$ 

=> $\frac{25}{2} [ -64]$

=>$\frac{- 1600 }{2} = - 800$ answer 

✰✰ hope it helps ✰✰

Answer 2

Answer is in attachment.