If ab = 21 and  then value of  is from Quantitative Aptitud

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 Multiple Choice QuestionsMultiple Choice Questions

31.

If straight a greater than straight b greater than 0 comma space space AB space equals space straight a minus straight b space cm comma space space space BC space equals space 2 square root of ab space cm comma space space then space angle ABC is

  • 45 degree
  • 60 degree
  • 90 degree
  • 90 degree
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32.

If ab = 21 and fraction numerator left parenthesis straight a plus straight b right parenthesis squared over denominator left parenthesis straight a minus straight b right parenthesis end fraction space equals space 25 over 4 then value of straight a squared plus straight b squared plus 3 ab is

  • 115

  • 121

  • 125

  • 125


B.

121

             ab = 21                         ...(i)
          fraction numerator left parenthesis straight a plus straight b right parenthesis squared over denominator left parenthesis straight a minus straight b right parenthesis squared end fraction space equals space 25 over 4
rightwards double arrow space space open parentheses fraction numerator straight a plus straight b over denominator straight a minus straight b end fraction close parentheses squared space equals space 25 over 4
rightwards double arrow space space space space space space fraction numerator straight a plus straight b over denominator straight a minus straight b end fraction space equals space 5 over 2
rightwards double arrow space space space space space 2 straight a plus 2 straight b space equals space 5 straight a minus 5 straight b
rightwards double arrow            3a = 7b
rightwards double arrow             straight a space equals space fraction numerator 7 straight b over denominator 3 end fraction                  ...(ii)
From equation (i),
                   fraction numerator 7 straight b cross times straight b over denominator 3 end fraction equals 21
                straight b squared space equals space 9
From equation (ii),
 straight a space equals space fraction numerator 7 cross times 3 over denominator 3 end fraction space equals space 7
therefore      straight a squared plus straight b squared plus 3 ab space equals space left parenthesis 7 right parenthesis squared plus left parenthesis 3 right parenthesis squared plus 3 cross times 7 cross times 3
                            =  49 +  9 + 63
                            = 121                  



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33.

Given, straight a minus straight b space equals space 2  and  straight a cubed minus straight b cubed space equals space 26 then left parenthesis straight a plus straight b right parenthesis squared is

  • 9

  • 4

  • 16

  • 16

130 Views

34.

If x + y + z = 9 then value of left parenthesis straight x minus 4 right parenthesis cubed plus left parenthesis straight y minus 2 right parenthesis cubed plus left parenthesis straight z minus 3 right parenthesis cubed minus 3 left parenthesis straight x minus straight y right parenthesis left parenthesis straight y minus straight z right parenthesis left parenthesis straight z minus 3 right parenthesis is

  • 6

  • 9

  • 0

  • 0

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35.

If straight a over straight b plus straight b over straight a equals negative 1, then the value of straight a squared over straight b squared minus straight b squared over straight a squared is

  • 1

  • -1

  • 0

  • 0

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36.

Among below expressions which one can be expressed as the difference of two cubic expressions?

  • straight x cubed plus straight y cubed plus 3 straight x plus 3 straight y
  • straight x cubed plus 2 straight x squared plus 3 straight x plus straight x squared
  • straight x cubed plus 3 straight x squared plus 3 straight x minus 2
  • straight x cubed plus 3 straight x squared plus 3 straight x minus 2
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37.

If straight a squared plus 1 over straight a squared space equals space 7 and V1 and V2 are the minimum and the maximum values of straight a cubed plus 1 over straight a cubed comma space then straight V subscript 2 minus straight V subscript 1 is equal to

  • -36

  • 36

  • 72

  • 72

107 Views

38.

If straight x plus fraction numerator 1 over denominator 9 straight x end fraction space equals space 4 comma then 9 straight x squared plus fraction numerator 1 over denominator 9 straight x squared end fraction is

  • 140

  • 142

  • 144

  • 144

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39.

If a = 2,  b = -3 then the value of 27 straight a cubed minus 54 straight a squared straight b space plus space 36 ab squared minus 8 straight b cubed is

  • 1562

  • 1616

  • 1676

  • 1676

95 Views

40.

If straight a cubed plus 1 over straight a cubed space equals space 2 comma space then value of fraction numerator straight a squared plus 1 over denominator straight a end fraction is (a is a positive number):

  • 1

  • 2

  • 3

  • 3

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