i don't see your problem, you basically said the solution, well, most of it anyway. yes, the derivative gives the slope at any point. you want the slope of the tangent line at the point x = -2 to find the equation of the tangent line at that point. you get a quadratic, that doesn't matter, just plug in x = -2 and solve. the number you get is the slope. use that to find the equation of the line