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[tex]find \: the \: sum \: of \: first \: 20 \: terms \: of \: \\ the \: series \\ 2 + 13 + 28 + 47 + 70.......[/tex]
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♡SOLUTION MUST
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Here,
Here,
a=2
D=13-2=11
So,
D=11
Also:-
n=20
Using the formula:-
S20=20/2.[2×2+{20-1}×11]
S20=10×(4+209)
S20=10×213
S20=2130