Ononot — A geometric sequence has a first term a1 and a common ratio

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Geometric Sequencesmedium

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A geometric sequence has a first term $a_1$ and a common ratio $r$ . If the sum of the first two terms is $S_2 = 12$ and the sum of the first four terms is $S_4 = 156$ , find the value of $r^2$ given $r$ is a real number.