Suppose you want to reach a point {{MATH_160}} that is located across the sand from a nearby road. {{CMD_161}} {{ENV_162}} {{CMD_163}} Suppose that the road is straight, and {{MATH_164}} is the distance from {{MATH_165}} to the closest point {{MATH_166}} on the road. Let {{MATH_167}} be your speed on the road, and let {{MATH_168}}, which is less than {{MATH_169}}, be your speed on the sand. Right now you are at the point {{MATH_170}}, which is a distance {{MATH_171}} from {{MATH_172}}. At what point {{MATH_173}} should you turn off the road and head across the sand in order to minimize your travel time to {{MATH_174}}? {{CMD_175}} Let {{MATH_176}} be the distance short of {{MATH_177}} where you turn off, the distance from {{MATH_178}} to {{MATH_179}}. We want to minimize the total travel time. Recall that when traveling at constant velocity, time is distance divided by velocity.