Question

What is the sum of the first 20 terms of an A. P., if a=4 and
$t{20} = 36$
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Answer 1

Answer:

S20 = 400

Step-by-step explanation:

Explanation is in the attachment

Hope this Helps !

Answer 2

Answer:

$a_{20}= 36, \: a=4, \: n=20 \\ S _{n} = \frac{n}{2} (a + a_{n}) \\ S _{20} = \frac{20}{2} (4 + 36) \\ S_{20} = 10 \times 40 \\ S_{20} = 400 \\Therefore, \: the \: sum \: of \: 20 \: terms \: is \: 400.$