Respuesta :

By using The half-angle formula

cos X/2 = ±√[(1 + cos X)/ 2]
But we have cos x=2/3
= ±√[(1 + 2/3)/ 2]
= ±√[(5/3 )/ 2]
= ±√[(5/5]
=±√1

Therefore answer is ±1

cos A/2 = ±√[(1 + cos A )/ 2]
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