Find the sum of first 40 terms of arithmetic sequence -2,-4,-6,8,
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Find the sum of first 40 terms of arithmetic sequence -2,-4,-6,8,
Find the sum of first 40 terms of arithmetic sequence -2,-4,-6,8,
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Answer:
[tex]S_{40}[/tex] = -1640
Step-by-step explanation:
[tex]S_{n}[/tex] = [2[tex]a_{1}[/tex] + (n-1) d] n/2
[tex]S_{40}[/tex] = [2 (-2) + (40-1) (-2)] 40/2
[tex]S_{40}[/tex] = [ -4 + (39) (-2)] 20
[tex]S_{40}[/tex] = [ -4 + (-78)] 20
[tex]S_{40}[/tex] = [-82] 20
[tex]S_{40}[/tex] = -1640