Question

if sin x = 0.5 what is the value of cos X?
round the value to the nearest thousandth

Answer 1

cos(arcsin(0.5)) = 0.866

Answer 2

Use the inverse button on your calculator in degree mode for this.  Inverse sin of .5 gives you an x value of 30 (30 degree angle, that is).  Now find the cos(30) and round.  cos(30) = .866