2x^2-12x+4=0
Divide through by 2: x^2-6x+2=0
Prepare to complete the square: x^2-6x=-2
Complete the square on the left-hand side: x^2-6x+9=-2+9=7 (add 9 to each side)
Square completed: (x-3)^2=7
Take square root of each side: (x-3)=±√7
x=3±√7, so x=5.646 or 0.354 approx.