1. The problem statement, all variables and given/known data Find two points on curve y=x4-2x2-x that have a common tangent line. 2. Relevant equations *the one stated above dy/dx = 4x3-4x-1 3. The attempt at a solution equation of a tangent line: y=mx+b (4x3-4x-1) = m at two different points? So there are two points for which dy/dx=4x3-4x-1 I'm not sure what thinking I should be doing on this one to link the information about there being two points in the curve with the same tangent line to what I know about finding tangent lines. Will the coordinate points contain x or can I find two actual, definite points? Aren't there more than 2 places on the curve with the same tangent lines?