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主要内容

有限的几何级数

问题

几何数列a, start subscript, i, end subscript定义如下:
a, start subscript, 1, end subscript, equals, 8
a, start subscript, i, end subscript, equals, a, start subscript, i, minus, 1, end subscript, dot, start fraction, 3, divided by, 4, end fraction
求数列的前25项之和。
选出正确答案:
不会做了?
不会做了?