Question

3. In an AP:
(1) given a =5, d=3, a'n = 50, find n and S
n'
​

Answer 1

a'n = a+ (n-1)d

50=5+(n-1)3

50-5=3n-3

45-3=3n

42=3n

42/3=n

14= n

Sn= n/2[2a+ (n-1)d]

= 14/2 [2×5+( 14- 1) 3]

= 7[10+( 13 ×3)]

=7[10+39]

=7[49]

=343

Hope this helps ✌✌