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Find the sum of first 20 terms of an AP ...

Find the sum of first 20 terms of an AP whose nth term is `4n-1`

Text Solution

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`a_n = 4n - 1`
`a_1 = axx1 - 1 = 3`
`a_2 = 4 xx 2 - 1 = 7`
`a_3 = 4 xx 3 - 1 = 11`
`d= 11-7= 7-3= 4`
`a=3`
`n= 20`
`S_n = S_20 = n/2[2a + (n-1)d]`
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