How many terms of the a.p. 9,17,25,....must be taken so that so their

1.	How many terms of the a.p. 9,17,25,....must be taken so that so their sum is 636
Answer» a=9,d=8,n=?,sn=636So sn=n/2(2a+n-1)d 636=n/2(18+n-1)8 313=n(144+8n-8) 313=n(136+8n) 313=136n+8n² 8n²+136n-313.

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