Question

P.A (2,½,...) S20?

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Answer 1

$r=\frac{1}{2}-2\\\\r=\frac{1}{2}-\frac{4}{2}\\\\r=-\frac{3}{2}\\\\a_{20}=2+(20-1).-\frac{3}{2}\\\\a_{20}=2+19.-\frac{3}{2}\\\\a_{20}=2-28,5\\\\a_{20}=-26,5$