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Aptitude Questions:

 

 

 

If 4a - 4/a+3=0, then the value of a3 – 1/a3 + 3 = ________

  • 3/16
  • 7/16
  • 21/16
  • 21/64
  • None of these
Answer- D

Given, 4a – 4/a + 3 =0

4a – 4/a = -3

=> 4(a-1/a) = -3

=> a-1/a = -3/4

Cubing on both sides,

=> (a-1/a)3 = (-3/4)3

=> a3  + 1/a3 – 3 x a x 1/a (a-1/a) = -27/64 => a3  + 1/a3 – 3 (a – 1/a) = -27/64

=> a3  + 1/a3 – 3 (-3/4)=-27/64 => a3  + 1/a3 + 9/4 + 3 – 3 =-27/64

=> a3  + 1/a3 + 3 + (9 – 12)/4 =-27/64 => a3  + 1/a3 + 3 =-27/64 + 3/4 = (-27 + 48)/64

=> a3  + 1/a3 + 3 =21/64.


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