If the sum of first 7 terms of an ap is 49 and that of 17 terms is 289 find the sum of n terms

If the sum of first 7 terms of an ap is 49 and that of 17 terms is 289

1.	If the sum of first 7 terms of an ap is 49 and that of 17 terms is 289 find the sum of n terms
Answer» 49=7/2[2a+6d]14=2a+6d7=a+3d_________134=2a+16d17=a+8d__________2a+3d=7a+8d=17______________on sub-5d=-10d=2a=1Sn=n/2{2+(n-1)2}Sn=n×n