# Geometric Sequence

Algebra Level 3

Suppose that all the terms of the geometric sequence $\{ a_n\}$ are positive. If $a_1a_2=a_{10}$ and $a_1+a_9 =20,$ what is the value of $(a_1+a_3+a_5+a_7+a_9)(a_1-a_3+a_5-a_7+a_9)?$

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