Explanation :
• To get coterminal angles you simply have to add or subtract 2 pi .
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• In this instance, we are looking for a coterminal angle between 0 and 2pi.
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• therefore we will add / subtract 2pi to 87pi /7 :
-2pi + (87 pi /7) = -(14 pi /7) + (87pi /7)
= 73pi /7