Question

Two APs have same common difference. If the first term is -1 and that of the other is -8. then the difference between their 4th term is?

Answer 1

7

Explanation:

Let the common difference of the two APs be" D"

Let 1st term of 1st AP be A₁ i.e = -1

And the first term of the second AP b₁ i.e = -8

We know that the nth term of an AP is;

an = a+(n-1)d

4th term of first AP,

a₁ + (4-1)d = − 1 + 3d. --Eqn. 1

And 4th term of the second AP,

b₁ + (4-1) d=-8+ 3d -- Eqn 2

Now, the difference between their 4th terms is i.e.

= (- 1+ 3d ) - (-8 + 3d )

= -1 + 3d + 8 - 3d = 7

So, the answer is 7.