Question

How many terms of AP. 9,17,25,...... Must be added to give a sum 72

Answer 1

a =9
d =17-9=8
Sn = n/2×{2a+(n-1)×d}
72=n/2×{2×9+(n-1)×8}
72=n/2×2×[9+4n-4]
72=n×(5+4n)
72=5n+4n^2
0=4n^2+5n-72 || b^2-4ac=D
|| 25-(-1152)=1177
-b±rootD/2a
-5±root 1177 /8

This is not possible, so sum can't come 72