Question

In an ap sum of first 6 term is 36 and sum of first 15 terms is 225 then find sum of first n terms​

Answer 1

Answer:

6a+15d=36 eq 1

30a+200d=450 ( divide eq by 10

3a+20d= 45

eliminate eq1 with 2

so, d=17/15 and a=19/6

sn= n/2(38/6+17/15)

Answer 2

Answer:

sum of first 6 terms is

3{2a+5d}=36

2a+5d=13

same as

15/2{2a+14d}=225

a+7d=15

2a+14d=30

subtact eq.

then

9d=17

d=17/9

a=16/9

ok

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