Question

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Answer 1

$a_{1}=-8\\\\d=-2\\\\a_{40}=a_{1}+39d=-8+39*(-2)=-8-78=-86\\\\\boxed{a_{40}=-86} \\\\\\2)a_{1} =2\\\\a_{7}=20\\\\S_{20}=? \\\\a_{7}=a_{1}+6d\\\\6d=a_{7}-a_{1}=20-2=18\\\\d=3\\\\S_{20}=\frac{2a_{1}+19d }{2}*20=(2a_{1}+19d)*10=(2*2+19*3)*10=61*10=610\\\\\boxed{S_{2}=610}$