This approximation is an {{CMD_16}}{{CMD_17}}overestimate{{CMD_18}}{{CMD_19}}underestimate{{CMD_20}}{{CMD_21}} because {{MATH_22}} is concave {{CMD_23}}{{CMD_24}}up{{CMD_25}}{{CMD_26}}down{{CMD_27}}{{CMD_28}} and the graph of {{MATH_29}} lies {{CMD_30}}{{CMD_31}}above{{CMD_32}}{{CMD_33}}below{{CMD_34}}{{CMD_35}} the graph of {{MATH_36}} near {{MATH_37}}.