Question

If 5 times the 5th term of an ap is equal to 8 term its 8th term then show that its 13 term is zero

Answer 1

5(a+4d)=8(a+7d)
5a+20d=8a+56d
-3a=36d
a=-12d
13th term
a+12d
-12d+12d=0
Hence proved.