3. In an AP:
(1) given a =5, d = 3, a, = 50, find n and S
(ii) given a = 7, 2,3 = 35, find d and Siz-
37 d = 3, find a and S 2.
Answers
Answer:
i) a=5 An= 50 n=?
d=3 S=?
An= a+ (n-1)d Sn= n/2[ 2a+(n-1)d]
50= 5+ (n-1) x 3 S16 = 16/2[ 2 x5 + (16-1) x 3]
50= 5+ 3n -3 = 8[ 10+15 x 3]
50= 2+ 3n = 8[10 +45]
3n = 50-2 = 8 x 55
3n = 48 S16 = 440
n = 48/3
n= 16
ii) a=7 A13=35
d=? S13= ?
An= a+ (n-1)d Sn=n/2[ a+l)
35= 7 + (13-1)d S13= 13/2 [ 7+ 35]
35= 7+ 12d = 13/2 x 42
12d= 35-7 = 13 x 21
12d= 28 S13 = 273
12d= 28
d= 28/ 12
d= 7/3
This answer is very simple in ex:5.3
I hope this answer helps for your understanding level.