Q. 6 I5.0( 1 Vote )

Which of the following list of numbers form A.R's? If they form an A.P., find the common difference d and also write its next three terms.

- 1.2, - 3.2, - 5.2, - 7.2, ...

Answer :

We have,


a2 – a1 = -3.2 – (-1.2) =-3.2 + 1.2 = -2.0


a3 – a2 = -5.2 – (-3.2) = -5.2 + 3.2 = -2.0


a4 – a3 = -7.2 – (-5.2) = -7.2 + 5.2 = -2.0


i.e. ak+1 – ak is the same every time.


So, the given list of numbers forms an AP with the common difference d = -2


Now, we have to find the next three terms.


We have a1 = -1.2, a2 = -3.2, a3 = -5.2 and a4 = -7.2


Now, we will find a5, a6 and a7


So, a5 = -7.2 + (-2) = -7.2 – 2.0 = -9.2


a6 = -9.2 + (-2) = -9.2 – 2.0 = -11.2


and a7 = -11.2 + (-2) = -11.2 – 2.0 = -13.2


Hence, the next three terms are -9.2, -11.2 and -13.2


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