Question

a8-? a1=8
s30-? d=-2

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Answer 1

$a_n=a_1+(n-1)d\Rightarrow a_8=8-2\cdot 7=8-14=-6$

$a_{30}=8-2\cdot 29=-50\Rightarrow S_{30}=\frac{a_1+a_{30}}{2}\cdot n=\frac{8-50}{2}\cdot 30=\frac{-42}{2}=-21\cdot 30=-630$