The sum of first q terms of an AP is 63q-3q^(2). if its p^(th) term is -60, find the value of p. also find the 11^(th) term of this AP.
Asked by Rohit Misra | 23rd Dec, 2013, 03:49: PM
Expert Answer:
Given Sq = 63q-3q2
S1 = 63 * 1 - 3* 1*1
=60 = a1
S2 = 63 * 2 - 3* 2 *2
=114
S2 - S1 = 114 - 60
=54 = a2
So, d = 54 - 60 = - 6
Now,
ap = - 60 (Given)
a + (p-1) d = - 60
60 + (p-1) (-6)= - 60
p-1 = -60-60 / -6 = 20
p = 21
Now,
a11 = a+ 10 d
=60 + 10 (-6)
= 60 + -60
= 0
Given Sq = 63q-3q2
S1 = 63 * 1 - 3* 1*1
=60 = a1
S2 = 63 * 2 - 3* 2 *2
=114
S2 - S1 = 114 - 60
=54 = a2
So, d = 54 - 60 = - 6
Now,
ap = - 60 (Given)
a + (p-1) d = - 60
60 + (p-1) (-6)= - 60
p-1 = -60-60 / -6 = 20
p = 21
Now,
a11 = a+ 10 d
=60 + 10 (-6)
= 60 + -60
= 0
Answered by | 23rd Dec, 2013, 06:09: PM
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