The geometric sequence a_ia i ​ a, start subscript, i, end subscript is defined by the formula: a_1 = -\dfrac13a 1 ​ =− 3 1 ​ a, start subscript, 1, end subscript, equals, minus, start fraction, 1, divided by, 3, end fraction a_i = a_{i - 1} \cdot (-3)a i ​ =a i−1 ​ ⋅(−3)a, start subscript, i, end subscript, equals, a, start subscript, i, minus, 1, end subscript, dot, left parenthesis, minus, 3, right parenthesis Find the sum of the first 757575 terms in the sequence.