Question

Find number of terms :
1 how many number of terms in ap 9,17,25.... taken so that tehier sum is 636?
2 how many number of terms in ap 63,60,57....taken so that their sum is 693?



pls ans asap
​

Answer 1

Step-by-step explanation:

1qn Solution

sn=636, a=9 d=8 ,n=?

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

636=n/2(18+8n-8)

636=n(5+4n)

4n^2+5n-636=0

4n^2-48n+53n-636=0

4n(n-12)+53(n-12)=0

n=-53/4,12

n value can't be negative so n=12,

our required terms is 12..

2)...

a=63,d=-3,n=?,Sn=693

Sn=n/2(126+(n-1)-3)

693 =n/2(126-3n+3)

693×2=n(129-3n)

1386=129n-3n^2

3n^2-129n+1386=0

3n^2-66n-63n+1386=0

3n(n-22)-63(n-22)=0

(3n-63)(n-22)=0

n=21,22

hope you understand

pls add as brainliest answer..and give one ❤️