10. a) Find the seventh term of a geometric sequence if the first term is 12 and the common ratio is 1 .25 b) The common ratio of a geometric series is 0.5 and the first term is 512. Find the sum of the first six terms c) Find the sum of the infinite geometric series 18 - 12 + 8 ............ 1 1 . a) Write in sigma notation the sum 7 + 1 - 5 ........ to eight terms b) Evaluate 23:13 x 1.5"