F(x) = (sqrt(29 + x) - x) / (x + 4)
a = -4
Perhaps Dunbar uses the image of a mask as wearing a face allows us to conceal our face - enabling us to hide any expression or emotion. In his poem, he mentions how black people felt the need to appear as content or happy when surrounded by people who were white - especially when they felt the opposite. The mask represents the false expressions the blacks had to wear.
