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| 1. |
Sum of 7 term 49 and sum of 17 term is 289 find sn |
| Answer» S7=7/2(2a+6d).49=7/2(2a+6d).2a+6d=49*2/7.2(a+3d)=14.a+3d=7.a=7-3d-------------(1).S17=17/2(2a+16d).289*2/17=2(a+8d).289/17=a+8d.a+8d=17---------------(2)Putting value of a in eq. (2).7-3d+8d=17.7-5d=17.-5d=10.d=-2.a=7-3*-2.a=13.Now,Sn=n/2(2a+(n-1)d).Sn=n/2(2*13+(n-1)-2).Sn=n(14-n). | |