Doing past papers at the mo & have a quadratic which I am stuck on

find fixed points of f(x) = x^2+(13/12)x-1/2

Now, fixed points are when f(x) = x, so I have subtracted x from both sides

=> x^2 + (1/12)x - 1/2 = 0 to make an easier(?) quadratic

so a=1, b=1/12 & c=-1/2

Sub into formula & I am now stuck as the sqrt comes up as negative & I'm not sure enough about completing the square.

I also have similar equation f(x) = x^2 + (14/15)x - 2/5. Stuck here, too

Would appreciate a little help.

Thank you