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The sum of first n terms of an A.P. is 5...

The sum of first n terms of an A.P. is `5n^2+3n` If its mth term is 168, (i) Find the value of m (ii) Find the 20th term of this AP

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`s_n = 5n^2 + 3n`
`s_1 = 5(1)^2 + 3 xx 1 = 8`
`s_2 = 5(2)^2 + 3 xx 2 =20 + 6 = 26`
`s_3 = 5(3)^2 + 3 xx 3 = 45 + 9 = 54`
`8, 18,28, ....`
`a= 8`
`d=18-8=10`
`T_m = a +(m-1)d= 168`
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