If {{MATH_42}} and {{MATH_43}} are differentiable, then {{MATH_44}} {{CMD_45}} We'll try to understand this geometrically. In what follows, the functions {{MATH_46}} and {{MATH_47}} look like lines; however, the young mathematician should realize that we are {{CMD_48}}not{{CMD_49}} looking at true lines, instead we are looking at {{MATH_50}} and {{MATH_51}} sufficiently ``zoomed-in'' so that they appear to be lines. First consider a graph of {{MATH_52}} with respect to {{MATH_53}}: {{CMD_54}} {{ENV_55}} {{CMD_56}} Now consider a graph of {{MATH_57}} with respect to {{MATH_58}}: {{CMD_59}} {{ENV_60}} {{CMD_61}} If we combine these graphs, by laying the graph of {{MATH_62}} on its side, we obtain: {{CMD_63}} {{ENV_64}} {{CMD_65}} Ah! From this we see that {{ENV_66}} so {{MATH_67}} {{CMD_68}} {{CMD_69}}