Two APs have the same common difference. The first term of one of these is - 1 and that of the other is - 8. The difference between their 4th terms is
Let a and A be the first terms of Two Aps
a = - 1
A = - 8
Let d and D be the common differences of two Aps
D = d ……..(i)
Let a4 and A4 be the 4th terms of two Aps
As we know, nth term of an AP is
an = a + (n - 1)d
where a = first term
an is nth term
d is the common difference
a4 -A4 = a + 3d – (A + 3D)
= a + 3d - A - 3d (using (i))
= a - A
= - 1 - (- 8)
= 7