Use sigma notation to represent the sum of the first six terms of the following sequence: 4, 12, 20, … the summation from n equals 1 to 6 of negative 4 plus 8 times n the summation from n equals 1 to 6 of 4 plus 8 times n the summation from n equals 1 to 6 of negative 1 plus 8 times n the summation from n equals 1 to 6 of 1 plus 8 times n