231k views
5 votes
Find the sum of a finite arithmetic sequence from n=1 to n=5 using the expression -3(4)^n-1

1 Answer

10 votes

Answer:

Explanation:

Arithmetic sequaence:


\sf a_n = -3(4)^n - 1\\\\a_1=-3*4^1 -1\\\\ = -3*4 - 1\\\\ = -12 - 1\\\\a_1=-13


a_2 = -3*4^2-1\\

= -3*16 -1

= -48 - 1

= -49

difference = second term - first term

= -49 -(-13)

= -49 + 13

d = -36


\boxed{S_n=(n)/(2)[2a + (n-1)d]}


\sf S_5=(5)/(2)*[2*(-13} + 4*(-36)]\\\\ =(5)/(2)[-26-144]\\\\=(5)/(2)*(-270)

= 5*(-135)

= -675

User Manjunath Reddy
by
8.2k points

No related questions found

Welcome to QAmmunity.org, where you can ask questions and receive answers from other members of our community.

9.4m questions

12.2m answers

Categories