For this question you need to use the circular arc length formula: s = r(theta). Here s is the arc length you are looking for . We know we are looking for arc length of part of a circle because the tip of the wiper is a constant distance away from a fixed center (the wiper base) (the geometrical definition of a circle is a collection of points on a plane that are the same distance away from a fixed center). Theta is the angle the wiper, or other radial line (line that goes out from the center of a circle), sweeps out as it rotates. We must be careful here, because for this formula theta must be in radians.
We know previously that one revolution (one sweep around the entire circle) is 360 degrees or 2pi radians (for general conversion between degrees and radians, use radians = degrees * pi / 180). This means that 0.25 revolution is 2pi / 4 = pi / 2 radians . The radius r of the circle we are tracing out is the length of the wiper, 24 inches. Plug the values into the formula s = r(theta) to get the arc length traced out by the tip of the wiper. Note that the units of the arc length that you get out are the same as the units of the radius that you put in.
