Calculate a, for the geometric sequence with a =4 and common ratio r = -2. O A. -8,192 O B. -512 O C. -256 O D. 256A geometric sequence has terms a; = 2 and a, = 128. Find the explicit formula for this sequence. O A. an = (2) "-1 O B. 1 22-1 a = 2 NI O C. an = = (2) "-1 O D. an : -(2) 23-1 4Calculate the missing terms of the geometric sequence .. ., 5, ?, ?, ?, 80, .... O A. 10, 20, 40 O B. 15, 30, 60 O C. 10, 30, 50 O D. 15, 45, 75