Originally Posted by

**BobP** Forget the derivative, you don't need it.

Suppose that the equation of the tangent line is $\displaystyle y=mx.$

Substitute this into your given equation and solve for $\displaystyle x.$

If the line is to be a tangent this has to give you equal roots, (so $\displaystyle b^2-4ac=0).$

It will also give you two values of $\displaystyle m.$

Incidentally, to be on the safe side, you should also sketch the graph of your original function, (it's a circle centre (2,0) radius 1), to confirm that your results make sense.