MATH HW HELP pleaseeee

Please help me work out these problems:

1) find the nth term of -200, 100, -50, 25

2) use sigma notation for 5+15+45+135+405

3)1+3+5+...+59 find the sum

4)2-1+1/2-1/4+...find the sum

5)1+4+4^2+...+4^8 find the sum

Problem 1)
A(n) = 25 (-1)^n 2^(4-n)

Problem 2)
........ 5
S = 5 ∑ 3^(k-1)
........ k=1

Problem 3)
...... 30
S = ∑ (2k -1) = 2 ( ½ ) (30) (31) - 30 = 900
..... k=1

Problem 4)
..... n
S = ∑ - (-1)^k 2^(2-k) = - (1/3) 2^(2-n) ( (-1)^n - 2^(n) )
..... k=1

Problem 5)
..... 9
S = ∑ 4^(k-1) = (1/3) (4^9 - 1) = 87381
..... k=1