Use implicit differentiation to find an equation of the line tangent to the curve $\displaystyle x^3 + 2xy +y^3 = 13$ at the point (1, 2).
2. $\displaystyle \begin{array}{l} x^3 + 2xy + y^3 = 13 \\ 3x^2 + \left[ {2y + 2xy'} \right] + 3y^2 y' = 0 \\ \end{array}$