2 1) Recall that sech(x) ex + e-x* second order partial derivatives: b) af 2 2f yx = Let f(x, y) = 2 sech(x - 4y). Find the [Hint: You may find that the algebra simplifies somewhat if you let tanh (x) = ex - e-x Then -sech(x) = -sech(x) tanh(x) and tanh(x) = sech(x).] d d ex + e-x dx dx