The sum of three numbers in G.P. is 21 and the sum of their squa

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 Multiple Choice QuestionsShort Answer Type

101.

If two G.M.'s <pre>uncaught exception: <b>mkdir(): Permission denied (errno: 2) in /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php at line #56mkdir(): Permission denied</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php line 56<br />#0 [internal function]: _hx_error_handler(2, 'mkdir(): Permis...', '/home/config_ad...', 56, Array)
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#6 {main}</pre> and one A.M. 'A' be inserted between two numbers, show that

2 straight A space equals space fraction numerator straight g subscript 1 superscript 2 over denominator straight g subscript 2 end fraction space plus space fraction numerator straight g subscript 2 superscript 2 over denominator straight g subscript 1 end fraction

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102.

If a be the A.M. and x, y be the two G.M.'s between b and c, show that

         straight x cubed plus straight y cubed space equals space 2 abc

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103.

The sum of first three terms of a G.P. is 13 over 12 and their product is -1. Find the terms.

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104.

The product of three numbers in G.P. is 125 and the sum of their products taken in pairs is 87 1 half. Find them.

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 Multiple Choice QuestionsLong Answer Type

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105.

The sum of three numbers in G.P. is 21 and the sum of their squares is 189. Find the numbers.


Let three numbers in G.P. be a, ar, ar2

Since the sum of the numbers is 21

∴                     a + ar + ar2 = 21                      rightwards double arrow      straight a left parenthesis 1 plus straight r plus straight r squared right parenthesis space equals space 21       ...(i)

Since the sum of the squares of the numbers is 189

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#6 {main}</pre>        rightwards double arrow     straight a squared left parenthesis 1 plus straight r squared plus straight r to the power of 4 right parenthesis space equals space 189        ...(ii)

Squaring both sides of (i), we get

                  straight a squared left parenthesis 1 plus straight r plus straight r squared right parenthesis squared space equals space left parenthesis 21 right parenthesis squared                                                          ...(iii)

Dividing (iii) by (ii), we get

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#6 {main}</pre>

rightwards double arrow     <pre>uncaught exception: <b>mkdir(): Permission denied (errno: 2) in /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php at line #56mkdir(): Permission denied</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php line 56<br />#0 [internal function]: _hx_error_handler(2, 'mkdir(): Permis...', '/home/config_ad...', 56, Array)
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#6 {main}</pre>                  rightwards double arrow      fraction numerator left parenthesis 1 plus straight r plus straight r squared right parenthesis squared over denominator left parenthesis straight r squared plus 1 right parenthesis squared minus straight r squared end fraction space equals space 7 over 3


rightwards double arrow     fraction numerator left parenthesis 1 plus straight r plus straight r squared right parenthesis squared over denominator left parenthesis straight r squared plus 1 plus straight r right parenthesis left parenthesis straight r squared plus 1 minus straight r right parenthesis end fraction space equals space 7 over 3               rightwards double arrow     <pre>uncaught exception: <b>mkdir(): Permission denied (errno: 2) in /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php at line #56mkdir(): Permission denied</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php line 56<br />#0 [internal function]: _hx_error_handler(2, 'mkdir(): Permis...', '/home/config_ad...', 56, Array)
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#6 {main}</pre>


rightwards double arrow              3 left parenthesis straight r squared plus straight r plus 1 right parenthesis space equals space 7 left parenthesis straight r squared minus straight r plus 1 right parenthesis         rightwards double arrow    4 straight r squared minus 10 straight r plus 4 space equals space 0

 
rightwards double arrow              2 straight r squared minus 5 straight r plus 2 equals 0                         rightwards double arrow   <pre>uncaught exception: <b>mkdir(): Permission denied (errno: 2) in /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php at line #56mkdir(): Permission denied</b><br /><br />in file: /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php line 56<br />#0 [internal function]: _hx_error_handler(2, 'mkdir(): Permis...', '/home/config_ad...', 56, Array)
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#6 {main}</pre>
When r = 2, from (i),

               straight a left parenthesis 1 plus 2 plus 2 squared right parenthesis space equals space 21                       rightwards double arrow                        a = 3

∴     Numbers are 3, 3(2), 3(2)2  or 3, 6, 12

When space space straight r space equals space 1 half comma space    from (i),

              straight a open parentheses 1 plus 1 half plus 1 fourth close parentheses space equals space 21                      rightwards double arrow                       a = 12

∴ Numbers are 12, space space 12 open parentheses 1 half close parentheses comma space space 12 open parentheses 1 half close parentheses squared   or 12, 6, 3


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106. Find four numbers forming a GP. in which the third term is greater than the first by 9 and the second term is greater than the fourth by 18.
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107. The sum of three numbers in GP. is 56. If we subtract 1, 7, 21 from these numbers in that order, we obtain an arithmetic progression. Find the numbers.
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108. The sum of three numbers which are consecutive terms of an A.P. is 21. If the second number is reduced by 1 and the third is increased by 1, we obtain three consecutive terms of a GP. Find the numbers.
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109. If pth, qth, rth and sth terms of an A.P. be in G.P., then prove that (p – q), (q – r), (r – s) are in GP.
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110. If a, b, c are in GP., prove that a2 + b2, ab + bc, b2 + c2 are also in GP.
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