In an ap a=1,an=20 and sn=399 what is the value of n?
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4
since ,
an = a+(n-1)d
20 = 1 + (n-1)d
19 = (n-1)d
also ,
Sn = n/2 {2a+19}
399 = n/2(21)
n = 38
an = a+(n-1)d
20 = 1 + (n-1)d
19 = (n-1)d
also ,
Sn = n/2 {2a+19}
399 = n/2(21)
n = 38
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2
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