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if a 1 =2 and a n -a n-1 =2n(n>=2), find the value of a 1 +a 2 +a 3 +.....+a 20.

if a1=2 and an-an-1=2n(n>=2), find the value of a1+a2+a3+.....+a20.

Grade:11

1 Answers

bhawani
33 Points
9 years ago
420
tn= 2 + { 4 + 6 + 8 + 10 + – – – –   + 19 terms}
=2 + 19/2{2.4 + (19 – 1 )2}
2 + 19/2{ 8 + 36}
=420

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