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

First you've got to get the linear term on the left side for this one ...

x^2-12x=-15

Now halve the linear coefficient, - 12/2=-6, now square that, 36, and add it to both sides of the equation ...

x^2-12x+36=21 now the left side is a perfect square ...

(x-6) ^2=21 take the square root of both sides ...

x-6=±√21 add 6 to both sides ...

x=6±√21

so x=6+√21 and 6-√21