1) Show that the derivative of the function xy = ex-y is log(x)/(log(xe))^2
2) Calculate the rate of increase of the height of a cone formed by sand pouring from a pipe when the height is 4cm.
3) Find the equation of the tangent line to the curve y = √3x - 2 that is parallel to the line 4x - 2y + 5 = 0.
4) Prove the identity tan-1(1) + tan-1(2) + tan-1(3) = π.