Question

यदि किसी समांतर श्रेणी का a=1, an= 20 और 5n=399 हो तो n= कितना होगा​

Answer 1

Step-by-step explanation:

73ueuegvvn2oeuruowvbdjeu3cebdnnsgehwivdvhegegbbueevvghhhhhhhhiejrv2jkhrgrijehhbbrhehhhhrhhhhheh

Answer 2

Answer:

Sn=399 , a=1, an=20 find n

formula: Sn= n/2(2a+(n-1)d)

399=n/2(2+(n-1)d) eq 1.

to find value of (n-1)d

we know an = a+( n-1)d

20=1+(n-1)d

(n-1)d=19 put the value in eq 1.

399=n/2(2+19)

399=n/2(21)

399*2/21=n

n=38 Answer