That is our approximation. Now we need to determine whether this value was an overestimate or an underestimate. {{MATH_187}} which is positive in the interval {{MATH_188}}. That means {{MATH_189}} is concave up on the interval {{MATH_190}} (since this interval is inside {{MATH_191}}). The approximation value is {{MATH_192}} which is an underestimate because {{MATH_193}} is concave up on the interval {{MATH_194}}. {{CMD_195}} {{CMD_196}}