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CBSE - X - Mathematics

Arithmetic Progression

Asked by 26th February 2009, 4:35 PM
Answered by Expert


Let the first term be a and the common difference be d.

Remember that two find two unknown quantities, we must have two equations involving them, which we'll solve and get the answer.

the first seven terms are

a,a+d, a+2d...a+6d

So their sum= (7/2)[a+a+6d]=(7/2)[2a+6d]


 according to question


This gives us


The next seven terms are


these terms can be thought of as in A.P. with first terms as a+7d and common difference as d.


So their sum =  (7/2)[a+7d+a+13d]=17

This gives us


Solving the two equations we get

the values of a and d.


Answered by Expert 27th February 2009, 3:00 PM

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