1 Answer

Shine · Answer 1 · 2019-05-15T04:22:31+0000

The common difference can be found from

d=(a_(17)-a_(7))/(17-7)=(81-41)/(17-7)=(40)/(10)=4

The first term of the sequence can be found from either of the given terms.

$a_(7)=41=a_(1)+(7-1)d=a_(1)+24\\a_(1)=41-24=17$

The sum of 40 terms is

$S_(40)=(40)/(2)(a_(1)+a_(40))=20(17+(17+39\cdot 4)=20\cdot 190=3800$

The sum of the first 40 terms is 3800.

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