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Since all the terms are positive and they are not all the same, determine the sum of the first twenty terms of the arithmetic progression in terms of $a$.
Mathematics 9709 · AS & A Level · Series
Series — practice question
The first term of the geometric progression and the first term of the arithmetic progression are each $a$. The third term of the geometric progression matches the second term of the arithmetic progression. The fifth term of the geometric progression matches the sixth term of the arithmetic progression.