Math, asked by Happy4457, 11 months ago

if an ap if a=1 an=20 and sn=42 <br />then n is​

Answers

Answered by radusdirectp8k8b8
0

please refer to the attachment!!

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Answered by MagicalGiggles
1

Given :-

  • a = 1
  • {a}_{n} = 20
  • {S}_{n} = 42

{S}_{n} = \frac{a \: + \: {a}_{n} \: }{ 2 } × n

  • 42 = \frac{ 1 \: + \: 20 }{ 2 } × n

  • 42 = \frac{ 21 }{ 2 } × n

  • 21 n = 42 × 2

  • n = \frac{ 42 \: × \: 2 }{ 21 }

  • n = { 2 \: × \: 2 }

\huge\fbox\green{ n \: = \: 4 }

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