Q. 484.2( 6 Votes )

The sum of first q terms of an A.P. is 63q – 3q2. If its pth term is-60, find the value of p. Also, find the 11th term of this A.P.

Answer :

Given that: Sq= 63q – 3q2

Put q = 1


S1 = T1 = 63 – 3 = 60


Put q = 2


S2 = 63 * 2 – 3 * (2)2


= 126 – 12 = 114


T2 = S2 – S1 = 114 – 60 = 54


Put q = 3


S3 = 63 * 3 – 3(3)2


= 189 – 27 = 162


T3 = S3 – S2


= 162 – 114 = 48


Therefore, first term of this A.P. is 60 and Common difference is 54 - 60 = -6


Tp = a + (p – 1) d


-60 = 60 + (p – 1) (-6)


-120 = (p – 1) (-6)


(p – 1) = 20


p = 21


Now 11th term of this A.P


T11 = 60 + (11 – 1) (-6)


= 60 – 60 = 0


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