Question

The sum of first 13 terms of and A.P 7,4......is:​

Answer 1

Answer:

here 1st term is a =7

common difference is 4-7= -3

sum of first 13terms is

13/2{2.7+(13-1).-3

=13/2{14+12. -3}

=13/2{14-36}

=13/2.(-22)

=13.(-11)

= -143

Answer 2

I hope this will be helpful to you..

⭐We will use formula:-

❗Sn = n/2 (2n+(n-1)d)❗

• But before that the value of unknown quantity are as follows :-

• d = -3 i.e. ( 4-7 )
• n = 13
• a = 7

Now, Sn = 13/2 (2*7+(13-1)*-3)

=. 13/2 (14-36)

= 13/2*(-22)

=. 13*(-11)

Sn = -143