Question

in an AP a=1 an=20 sn=441 then find n

Answer 1

hope u can understand it

Answer 2

Here your answer goes

Step :-1

Given ,

An = 20

First term of an AP ( a ) = 1

Sn = 441

By using the formula

$a_{n}$ = a + (n- 1 ) * d

20 = 1+ ( n-1 ) * d

20 - 1 = ( n - 1 ) * d

19 = ( n - 1 ) * d

Step :- 2

We have formula for Sum of n terms as below :-

$S_{n} = \frac{n}{2} ( a + ( n -1 ) * d )$

Put the value

441 = n/2 ( 2+ ( n- 1) * d )

==>> 882 = n  ( 2 + 19 )

===>> 882 = n ( 21 )

===>> 882/21 = n

====>> 42 = n

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