Solve x2 = 12x – 15 by completing the square. which is the solution set of the equation?


Asked by wiki @ in Mathematics viewed by 425 People

Answered by wiki @


For this case we have the following polynomial:
  x ^ 2 = 12x - 15

The first thing to do is to place the variables on the same side of the equation.
We have then:
  x ^ 2 - 12x = -15

We complete the square by adding the term (b / 2) ^ 2 on both sides of the equation.
We have then:
x ^ 2 - 12x + (-12/2) ^ 2 = -15 + (-12/2) ^ 2

Rewriting we have:
x ^ 2 - 12x + (-6) ^ 2 = -15 + (-6) ^ 2

x ^ 2 - 12x + 36 = -15 + 36
 
(x-6) ^ 2 = 21
x-6 =+/- \sqrt{21}
Therefore, the solutions are:
x = 6 - \sqrt{21}
x = 6 + \sqrt{21}
Answer:
the solution set of the equation is:
x = 6 - \sqrt{21}
x = 6 + \sqrt{21}

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