The TRIG package also makes your programs more portable because it can be used as a standard math package. You were probably surprised when you discovered Ada has no predefined math package. That may seem strange for a military programming language, but it makes good sense. Since Ada is strongly typed you would have to have separate math function for every real data type. Since the number of distinct real data types is unbounded, that would be a lot of math routines.
Some machines have an optional math coprocessor.
Ada would have to have multiple versions of the math library, some of which would use the coprocessor and others wouldn't. Furthermore, some applications may need immediate answers good to three decimal places, while other applications need higher precision and have all the time in the world to compute the answer. These are all good reasons for leaving the math routines out of the Ada language. I wouldn't have it any other way. Compiler vendors, however, wisely recognized that most of us programmers use math functions often in our application programs.