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The common difference ‘d’ of the A.P. in which T_7 = 9   and  T_1 T_2 T_7   is least, is

Option: 1

16


Option: 2

43955


Option: 3

1.65


Option: 4

none


Answers (1)

best_answer

 

General term of an A.P. -

T_{n}= a+\left ( n-1 \right )d

- wherein

a\rightarrow First term

n\rightarrow number of term

d\rightarrow common difference

 

 

a + 6d = 9

            T_1 T_2 T_7 = a(a + d) (a + 6d) 

                = 9a (a + d) = 9( 9-6d) (9-5d)       

             T_7 = a+ 6d = 9

            Let A =T_1 T_2 T_7 

            \frac{dA }{d(d)}=9[-45-54+60d]=0 

            60 d = 99

            d =33/20

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