Question

If the nth term of an A.P. is (5n-3),find the sum of first 20 terms of the A.P. using the formula​

Answer 1

Answer:

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Step-by-step explanation:

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Answer 2

$Given \: n^{th} \:term \:of \: an \:A.P :\\</p><p>a_{n} = 5n - 3$

$i )First \:term (a_{1}) = 5\times 1 - 3 \\= 5 - 3 \\= 2$

$iii )20^{th} \:term (a_{20}) = 5\times 20- 3 \\= 100 - 3 \\= 97$

$\boxed { \pink { Sum \:of \: n \:terms S_{n} = \frac{n}{2}(a + a_{n} ) }}$

$Here, a = 2, a_{20} = 97 , n = 20$

$\red { Sum \: of \: 20 \:terms (S_{20}) } \\= \frac{20}{2} ( 2 + 97 ) \\= 10 \times 99 \\= 990$

Therefore.,

$\red { Sum \: of \: 20 \:terms (S_{20}) }\green {= 990 }$

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