I were reading Calculus notes and I found out that when pi is used as an angle of a trigonometric function it's value is 180 degrees and when the same pi is outside that function its value changes to 22/7= 3.14.......aprx

like cos(pi) = x ------> cos(180drgrees) = x

but also cos(pi) = x -------> 3.14.....aproximately = arccos(x)

Why?????