here is the problem i was trying to do: A baseball player stands 2 feet from home plate and watches a pitch fly by. Find the rate D(theta)/dt at which his eyes must move to wach a fastball with dx/dt=-130 ft/s as it crosses homeplate at x=0. now there is a nice diagram of a right trianlge with x labled as the distance from the ball from the plate and theta as the angle from the player's eyes to the ball. where i'm confused is how exactly i relate these. not sure what trig function to use, or then how to solve it. also what would be some general rules to follow when solving any related rate problem involving an angle? PS: this is not a hw problem, but rather on i was trying to solve for fun, so i'm not really interested in the answer but more of how you solve it.