Question

In an A.P 4 times 4th term = 5 times 5th term then _____ term is 0

Answer 1

4×a4 =5×a5

4(a+3d)=5(a+4d)

4a+12d=5a+20d

4a-5a=20d-12d

-a=8d

a=-8d

a+(n-1)d=0

-8d+(n-1)d=0

-8d+dn-d=0

-9d=-dn

9d=dn

n=9

so the 9 th term of ap is 0