Answer
$-21846$
Work Step by Step
Here, $a_1=-2, r=-2, n=15$
Now, we have
$S_n=\dfrac{a_1(1-r^n)}{1-r}$
Now,
$S_{15}=\dfrac{(-2)(1-(-2)^{15})}{1-(-2)}$
or, $=-21846$
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