If a, b, c are in A.P. and x,y,z are in G.P., show that  from

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 Multiple Choice QuestionsShort Answer Type

111. If a, b, c, d are in GP., show that (a2 + b2 + c2) (b2 + c2 + d2) = (ab + bc + cd)2
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 Multiple Choice QuestionsLong Answer Type

112.

If a, b, c are in G.P. and x, y are the arithmetic means of a, b and b, c respectively,

then prove that   straight a over straight x plus straight c over straight y equals 2 and space space 1 over straight x plus 1 over straight y equals 2 over straight b

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113.

If a, b, c are in A.P. and x,y,z are in G.P., show that 

straight x to the power of straight b minus straight c end exponent. space straight y to the power of straight c minus straight a end exponent. space straight z to the power of straight a minus straight b end exponent space equals space 1



Since a, b, c are in A.P.

∴              b - a = c - b rightwards double arrow2b = c + a

Here, x, y, z are in G.P.

Let r be the common ratio

∴               y = xr, z = xr2

Now, space space space space space space straight x to the power of straight b minus straight c end exponent. space straight y to the power of straight c minus straight a end exponent. space straight z to the power of straight a minus straight b end exponent space equals space straight x to the power of straight b minus straight c end exponent left parenthesis xr right parenthesis to the power of straight c minus straight a end exponent. space left parenthesis xr squared right parenthesis to the power of straight a minus straight b end exponent space equals space straight x to the power of straight b minus straight c end exponent. space straight x to the power of straight c minus straight a end exponent. space straight r to the power of straight c minus straight a end exponent. space straight x to the power of straight a minus straight b end exponent. space straight r to the power of 2 straight a minus 2 straight b end exponent.

                                    equals space straight x to the power of straight b minus straight c plus straight c minus straight a plus straight a minus straight b end exponent. straight r to the power of straight c minus straight a plus 2 straight a minus 2 straight b end exponent space equals space straight x to the power of 0. straight r to the power of straight c plus straight a minus 2 straight b end exponent

                                     equals straight x to the power of 0. space straight r to the power of 2 straight b minus 2 straight b end exponent space equals space 1. space straight r to the power of 0                                       [By using (i)]

                                      = 1 . 1 = 1

∴    straight x to the power of straight b minus straight c end exponent. straight y to the power of straight c minus straight a end exponent. straight z to the power of straight a minus straight b end exponent equals space 1
                                    

                    

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114. Find a GP. for which sum of first two terms is –4 and fifth term is 4 times the 3rd term.
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115. If A.M. and G.M. of roots of a quadratic equation are 8 and 5 respectively, then obtain the quadratic equation.
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 Multiple Choice QuestionsLong Answer Type

116. If a and b are roots of x2 – 3x+p = 0 and c, d are roots of x2 – 12x + q = 0 where a, b, c, d form a GP., prove that (q + p) : (q – p) = 17 : 15
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117. Find four numbers in GP. whose sum is 85 and product is 4096.
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 Multiple Choice QuestionsShort Answer Type

118. Find the sum of n terms of the series whose nth term is given by 

straight n squared plus 2 to the power of straight n
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 Multiple Choice QuestionsLong Answer Type

119.

Insert 5 G.M.'s between 32 over 9 space and space 81 over 2

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120.

Find the sum of first n natural numbers  Or

Evaluate sum straight n space or space sum from straight k equals 1 to straight n of space straight k

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