In an AP given a=(-4), d=3; find its 20th term and sum of first 20 terms
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Answer:
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Step-by-step explanation:
Given: a=(-4), d=3
t=a+(n-1)d
=-4+(20-1)3
=-4+19×3
=-4+57
=53
Therefore, the 20th term =53
S=n [ 2a+(n-1)d]
2
=20 [2×(-4)+(20-1)3]
2
=10 [-8+19×3]
=10 [-8+57]
=10×49
=490
therefore, sum of first 20 terms is 490
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