Question

if 4 term of an ap is zero prove that a25 is three times a11

Answer 1

Answer of this question is

Answer 2

A4 = 0
a +3d =0......1

To prove
A25 = 3A11
lhs = a25 = a + 24d = a +3d + 21d
= 0 + 21d
= 21d
Now
rhs = 3a11
= 3(a +10d)
3a + 30d
= 3a + 9d +21d
=3(a +3d)+21d
3*0 + 21d.
= 0 + 21d
= 21d.
Thus lhs=rhs
Hence proved A25 = 3A11