1.

If the sum and product of the first three terms in an A.P. are 33 and 1155, respectively, then a value of its 11th term is : (1) –25  (2) –35  (3) –36  (4) 25 

Answer»

Correct option  (1) –25 

Explanation:

Let the three numbers in A.P. are 

a – d, a, a + d

given that : a – d + a + d = 33

 a = 11

and (a – d)(a)(a + d) = 1155

 a(a2 – d2 ) = 1155

 11(121 – d2 ) = 1155

 d2 = 16

 d = ±4

If d = 4 then first term a – d = 7 

If d = –4 then first term a – d = 15 

T11 = 7 + 10(4) = 47

or T11 = 15 + 10(–4) = –25



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