Answer
$10$
Work Step by Step
$\sum ^{4}_{i=1}\left( -2\right) ^{i}=\dfrac {a_{1}\left( r^{n}-1\right) }{r-1}=\dfrac {\left( -2\right) \times \left( \left( -2\right) ^{4}-1\right) }{-2-1}=10$
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