Question

if the sum of first 15 terms of an AP is 675 and its first term is 10 then find 25th term​

Answer 1

we have,

a=10

s15=675

we know that,

sn=n/2{2a+(n-1)d}

so,

675= 15/2{2×10+(15-1)d}

675=15/2(20+14d)

675=15/2×20+15/2×14d

675= 150+105d

675-150=105d

525=105d

5=d

Now,

an25= 10+ (25-1)5

=10+120

= 130

Hence, 25th term of an is 130.

I hope it will help you lot.

Answer 2

Answer:

Step-by-step explanation:

Here., Sn= 675

n =15

a=10

To find 25th term

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

675=15/2(2(10) +(15-1) d)

675 =7.5(20+14d)

675=150+105d

675-150=105d

525 =105d

d=5

Now, a25 = a+(n-1) d

=10+(25-1) 5

=34(5)

=170

Therefore, a25th term is 170