Respuesta :

CastleRook
The sum notation for the series given will be found as follows:
3 - 15 + 75- 375 ...
the common ratio is:
-15/3=-5

the first term is:
a=3
thus the summation notation will be:
Sn=(from i=1 to n)∑a(-5)⁽ⁿ⁻¹⁾