My professor started lecture about integrals with sigma notation...i'm having trouble figuring out how to write the following in sigma notation:

1. 3/5 + 4/6 + 5/7 + 6/8 + 7/9

2. 1-a+a^2-a^3+a^4-a^5+...+(-1)^n a^n

For number one I see the pattern but can't make out the right sum notation.

For number two i got k=0 sigma to n a^k(-1)^k but its wrong I think.

Any help would be great...