In the equation {{MATH_22}}, when {{MATH_23}} is very close to {{MATH_24}}, all of the terms will be very small, but the term {{MATH_25}} will be small even compared to {{MATH_26}}. So the curve should look a lot like the curve {{MATH_27}} close to {{MATH_28}}. But {{MATH_29}} is equivalent to {{MATH_30}}, which is exactly the pair of lines {{MATH_31}} and {{MATH_32}}. {{CMD_33}} {{CMD_34}}