JEE Math Practice Question
If each term of a geometric progression $$a_1, a_2, a_3, \ldots$$ with $$a_1=\frac{1}{8}$$ and $$a_2 \neq a_1$$, is the arithmetic mean of the next two terms and $$S_n=a_1+a_2+\ldots . .+a_n$$, then $$S_{20}-S_{18}$$ is equal to
- A.$$-2^{15}$$
- B.$$2^{15}$$
- C.$$-2^{18}$$
- D.$$2^{18}$$
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