Answers

2016-02-14T13:55:46+05:30
Here a=9 &d=17-9=8
sn=n/2 (2a+(n-1)d)
450=n/2 (18+(n-1)8)
900=n (18+(n-1)8)
900=n (10+8n)
900/n=10+8n
900-8n^2/n=10
900-8n^2=10n
8n^2+10n-900=0
solve this equation by quadratic formula .
u will get n=10
got it?
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