Q. 145.0( 1 Vote )

The 7th term of an A.P. is – 4 and its 13th term is – 16. Find the A.P. [CBSE 20041

Answer :

We have


a7 = a + (7 – 1)d = a + 6d = –4 …(1)


and a13 = a + (13 – 1)d = a + 12d = –16 …(2)


Solving the pair of linear equations (1) and (2), we get


a + 6d – a – 12d = –4 – (–16)


– 6d = –4 + 16


– 6d = 12


d = –2


Putting the value of d in eq (1), we get


a + 6(–2) = –4


a – 12 = –4


a = 8


Hence, the required AP is 8, 6, 4, 2,…


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