[tex] This is what i have so far, I know that y = mx + b and therefore y = -1x + k. and that to set the y values equal to each other to get; 1/x-1 = -1x + k. Then I get stuck on rearranging this equation so that it equals zero, I know schoolgirl error, once the equation is rearranged i can use the discriminant part of the quadratic equation to solve for k, (b^2 - 4ac), when this equals zero there is just one solution to the quadratic, right. But it is just that rearranging part that is getting me stuck, im not sure off it.[/QUOTE]
Since you know the slope of the tangent line is -1, you know the derivative of y must be -1 at that point. For what x is the derivative -1?