Question

find the sum of the following series
1-3+9-27+.....upto 9 terms​

Answer 1

Answer:

4921

Step-by-step explanation:

1-3+9-27+.....upto 9 terms​

1 + (-3) + (-3)² + .. 9 terms

here a= 1 ;  r = -3 ; n =9

=> S₉ =  $\frac{1*(1-(-3)^9)}{(1-(-3)}$

         =  $\frac{(1-(-19683))}{(1+3)}$

         =  $\frac{(1+19683))}{(4)}$

         = $\frac{19684}{4}$

         = 4921