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Triangle ABC is a right triangle. Write down Pythagoras theorem for this triangle and solve for r. The length of the arc AD is given by r θ where θ is the measure of the angle DCA in radians. Since tan(θ/2) = (c/2)/(r  h) you can use your calculator to find θ = 2 tan^{1}[(c/2)/(r  h)]. (Make sure you have your calculator on radians not degrees.) Thus the length of the arc is
I hope this helps,  


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