Write each series in summation notation:

*this is the only one that i cant solve

-2+4+(-6)+8+(-10)+12
Please help! :(

2 answers

Had they all been positive, then it would be
∑ (2n) from n=1 to 6
but they alternate + - , so you need a multiplier that flip-flops between ±
how about (-1)^n, if n is odd you get a negative, if n = even you get a positive, so ....

∑ (2n)(-1)^n from n=1 to 6
Thanksssss