Write the series in sigma notation

Question

10.     2 + 12 + 72 + 432 + 2592 + 15552

 

11.    1 + 27 + 23 + ... - 5

 

12.     2 - 10 + 50 - 250 + 1250 ...

Answer 1

10. Terms are 2, 2*6, 2*6*6, 2*6^3, 2*6^4, ..., 2*6^k where k=0 to n: 2∑6^k for k=0 to n.

11. 1+27+27-4+27-8+...+27-32+...; this is 1+∑27-4k where k=0 to n, where n=8 if -5 is the last term.

12. Every other term is negative, so we can use (-1)^k to alternate between + and -; 2∑(-1)^k*5^k where k=0 to n.