How do you calculate $sin{(1/2) arccos (4/5)}$ ?

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Answer 1 · 2015-11-04T16:38:40

Calculate $sin {(1/2)arccos (4/5)]$

Ans: $+- 0.32$

Use calculator.
$cos x = 4/5 = 0.8$ --> arc $x = +- 36^@87$
Arc $x/2 = +- 18^@43$ .
$sin (+-18.43) = +- 0.32$

How do you calculate sin{(1/2) arccos (4/5)}sin{(1/2) arccos (4/5)}?