Given the following two formulas for an arithmetic sequence, which of the statements below are true? check all that apply. the explicit formula: an = a1 + (n - 1) • d the recursive formula: an = an-1 + d. a. a1 is the previous term in the sequence b. a1 is the first term in the sequence c. an-1 is the nth term in the sequence d. n is the index of the sequence e. an is the previous term in the sequence