Motion makes this very easy, Create a line using the Bezier, B-Spline or paint tool. I like the B-Spline tool. Go to the Shape tab in the Inspector. Go to the Start or End Cap option. Change Round to Arrow and you have an arrow head. Change the Arrow head length with the Arrow Length slider and the width with the Arrow Width slider. Feel Free to ad a Write on Behavior and the arrow will animate with the right on. Best of luck.
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