Question

The sum of first 18 terms of an ap is 100 and sum of first 19 terms is 551 find ap

Answer 1

Answer:

t18 = a+(18-1)d

100 = a+17d

i.e, a+17d = 100__(i)

t19 = a +(19-1)d

551 = a +18d

i.e, a+18d = 551__(ii)

subtracting equation (i) & (ii)

a + 18d = 551

- a + 17d = 100

__________

d = 451

substitute d = 451 in equation (i)

a + 17×451 = 100

a + 7667 = 100

a = 100 - 7667

a = -7567

Answer 2

Answer:

t18 = a+(18-1)d

100 = a+17d

i.e, a+17d = 100__(i)

t19 = a +(19-1)d

551 = a +18d

i.e, a+18d = 551__(ii)

subtracting equation (i) & (ii)

a + 18d = 551

- a + 17d = 100

__________

d = 451

substitute d = 451 in equation (i)

a + 17×451 = 100

a + 7667 = 100

a = 100 - 7667

a = -7567

Explanation:

Hope this answer will help you.✌️