Question

If double the second term of an A.P is equal to 5 times its fifth term. Then show that 7th term of A.P is zero.....

Answer 1

Given: 2(a2)=5(a5)
So, 2(a+d)=5(a+4d)
2a+2d=5a+20d
-3a=18d
a=-6d
To prove : a7=0
a+6d=0
-6d+6d=0
0=0

Answer 2

2a+2d=5(a+4d)
2a+2d=5a+20d
2a-5a=20d-2d
-3a=18d
a= -6d

a+6d=0
-6d+6d=0
0=0