Rewrite: x^2-6x-4=0 as a quadratic. Solve using the formula: x=(6±√(36+16))/2=3±√52/2=3±√13.
So the solution is x=3+√13=6.6056 approx, and 3-√13=-0.6056 approx.
You can also solve by completing the square:
x^2-6x+9=4+9; (x-3)^2=13; x-3=±√13 and x=3±√13, as above.