Question

For an A.P. t1 = 2, tn = 41 and Sn = 860. What is the value of n ? *​

Answer 1

Given :

Sn =860

t1 = 2

tn = 41 , tn = [a +( n-1 )d ]

and we have find

n =?

SN = n/2 (2a + {n-1}d ) = 860

n/2( 2× 2+ (n-1)d ) = 860

n/2 (tn+t1) = 860

n/2 (41 +2) = 860

n/2 (43) = 860

n = (860 ×2 )/43

n = 40

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