Question

for an given A.P a=15 d=7 and an= 148 find n and Sn​

Answer 1

Answer:

an=148

a+(n-1)d = an

15 +(n-1) 7 =148

(n-1)7=148-15

(n-1)7=133

n-1=133/7

n-1 = 19

n=19+1

n=20

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

sn=20/2[2×15+(20-1)7]

sn=10[30+133]

sn=10×163

sn=1630