+130503 cosx =1/9 what is the value of cos 1/2x
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Using the identity cos [x/2] = ±SQRT [(1 +cos(x) / 2] = ±SQRT [(1 + (1/9) / 2] = ±SQRT [5/9] =
±SQRT (5) / (3)
If x lies in the first quadrant, take the positive root; if x lies in the fourth quadrant, take the negative root.
