题目
Problem
The third term of a geometric progression is 18 and the sum of the first three terms is 26. It is given that the common ratio is negative.
(a) Find the tenth term of the progression. Give your answer correct to 3 significant figures.
[5]
(b) Find the exact value of the sum to infinity of the progression.
[2]
题目中文翻译
一个等比数列的第三项为 18，前三项之和为 26。已知公比为负。
(a) 求该数列的第 10 项。答案精确到 3 位有效数字。
[5]
(b) 求该数列无穷和的精确值。
[2]