UPSEE Solved Model Paper 1

ak−1 =

ak+ak−2

2

⇒ a1,a2,...,a11 are in A.P.
Let d be the common difference of A.P.
Σr=010(5+rd)2 = 990 ⇒ 152 × 11 + d2×

10×11×21

6

+ 30d×

10×11

2

= 990
⇒ 7s2+30d+27 = 0 ⇒ d = - 3 or −

9

7

a2 = 15 + d = 12 or

96

7

But a2 <

27

2

⇒ d = - 3
S11 =

11

2

(2×15+10×−3) = 0