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Easy

Question

Let a subscript 1 end subscript comma a subscript 2 end subscript horizontal ellipsis.. a subscript 10 end subscript be A.P and h subscript 1 end subscript comma h subscript 2 end subscript horizontal ellipsis h subscript 10 end subscript be in H.P If a subscript 1 end subscript equals h subscript 1 end subscript equals 2 and a subscript 10 end subscript equals h subscript 10 end subscript equals 3 the a subscript 3 end subscript h subscript 8 end subscript equals

  1. 2/3    
  2. 4    
  3. 9    
  4. 6    

hintHint:

The harmonic progression is formed by taking the reciprocal of the terms of the arithmetic progression. If the given terms of the arithmetic progression are a, a + d, a + 2d, a + 3d, ...., then the terms of the harmonic progression (or harmonic sequence) are 1/a, 1/(a + d), 1/(a + 2d), 1/(a + 3d), 1/(a + 4d),...... Here a is the first term and d is a common difference. Both a and d have non-zero values.

The correct answer is: 6


    Given : a subscript 1 end subscript comma a subscript 2 end subscript horizontal ellipsis.. a subscript 10 end subscript are in AP and h subscript 1 end subscript comma h subscript 2 end subscript horizontal ellipsis h subscript 10 end subscript are in HP
    Also : a subscript 1 end subscript equals h subscript 1 end subscript equals 2 and a subscript 10 end subscript equals h subscript 10 end subscript equals 3
    To Find : a subscript 3 h subscript 8
    a subscript 10 space equals space end subscript a subscript 1 space plus space 9 d space................ space left parenthesis space a subscript n space equals space space a space plus left parenthesis n minus 1 right parenthesis d right parenthesis

h e r e space a subscript 1 space equals space space 2 space a n d space a subscript 10 space equals space 3. space S u b s t i u t i n g space t h e s e space v a l u e s

rightwards double arrow 2 space plus space 9 d space space equals space 3
rightwards double arrow 9 d space equals space 1
rightwards double arrow d space equals space 1 over 9 space
N o w comma space a subscript 3 space equals space a space plus space 2 d space.................. space left parenthesis space a subscript n space equals space space a space plus left parenthesis n minus 1 right parenthesis d right parenthesis
S u b s t i t u t i n g space t h e space v a l u e s

a subscript 3 space equals space 2 space plus space 2 cross times 1 over 9 space equals space 20 over 9 space.............. left parenthesis 1 right parenthesis
    We know that in Harmonic Progression  the terms of the harmonic progression (or harmonic sequence) are the reciprocal of the terms of the arithmetic progression.
    If, h subscript 1 end subscript comma h subscript 2 end subscript horizontal ellipsis h subscript 10 end subscript are in HP
    rightwards double arrow 1 over h subscript 1 space comma space 1 over h subscript 2 comma space......... space comma space 1 over h subscript 10 space space a r e space i n space A P

h subscript 1 space equals space space 2 space a n d
h subscript 10 space equals space 3

rightwards double arrow 1 over h subscript 10 space equals space 1 over h subscript 1 space plus space 9 d subscript 1
S u b s t i t u t i n g space t h e space v a l u e s comma space w e space g e t

rightwards double arrow 1 third equals space 1 half space plus space 9 d subscript 1
rightwards double arrow d subscript 1 space equals space minus 1 over 54

N o w comma space 1 over h subscript 8 space equals space 1 over h subscript 1 space plus space 7 d subscript 1
S u b s t i t u t i n g space t h e space v a l u e s comma space w e space g e t

rightwards double arrow 1 over h subscript 8 space equals space 1 half space plus space 7 open parentheses negative 1 over 54 close parentheses

rightwards double arrow 1 over h subscript 8 space equals space 1 half space minus space 7 over 54

rightwards double arrow 1 over h subscript 8 space equals space 20 over 54 space equals space 10 over 27

rightwards double arrow h subscript 8 space equals space 27 over 10 space......... space left parenthesis 2 right parenthesis

F r o m space left parenthesis 1 right parenthesis space a n d space left parenthesis 2 right parenthesis

a subscript 3 h subscript 8 space equals space 20 over 9 cross times space 27 over 10 space equals space 6

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