First, we {{CMD_114}}introduce the variables{{CMD_115}} {{MATH_116}}, {{MATH_117}}, and {{MATH_118}}, denoting the distance of cyclist {{MATH_119}} from the point {{MATH_120}}, the distance of cyclist {{MATH_121}} from the point {{MATH_122}}, and the distance between the two cyclists, in that order. We {{CMD_123}}identify{{CMD_124}} the given rates {{MATH_125}} km/h, {{MATH_126}} km/h, when {{MATH_127}} and the unknown rate {{MATH_128}}, when {{MATH_129}}. Now, we {{CMD_130}}draw a picture{{CMD_131}}. {{CMD_132}} {{ENV_133}} {{CMD_134}} We {{CMD_135}}find equations{{CMD_136}} relating the variables {{MATH_137}}, {{MATH_138}}, and {{MATH_139}}. By the Pythagorean Theorem, {{MATH_140}} Since {{MATH_141}}, {{MATH_142}}, and {{MATH_143}} are functions of time, we {{CMD_144}}differentiate{{CMD_145}} both sides of the equation with respect to {{MATH_146}}. {{MATH_147}} This equation holds on some time interval, and , in particular, at the instant when {{MATH_148}} and {{MATH_149}}. Therefore, at that instant,