Which constant should be added and subtracted to solve the quadratic equation by completing square method?

Which constant should be added and subtracted to solve the quadratic equation `4"x"^2 - sqrt3"x" - 5` = 0 by the method of completing the square?

  • `9/16`

  • `3/16`

  • `3/4`

  • `sqrt3/4`

`3/16`

Explanation:

This can be written as

`4"x"^2 - sqrt3"x" - 5` = 0

`(2"x")^2 - 2 xx (2"x") xx sqrt3/4 - 5 + (sqrt3/4)^2 - (sqrt3/4)^2` = 0

`(2"x")^2 - 2 xx (2"x") xx sqrt3/4 + (sqrt3/4)^2 - 5 - 3/16` = 0

`(2"x" - sqrt3/4)^2 = 5 + 3/16`

`(2"x" - sqrt3/4)^2 = 83/16`

Hence the given equation can be solved by adding and subtracting `3/16`.

Concept: Solutions of Quadratic Equations by Completing the Square

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