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

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