Difference between 'in order to', 'so as to,' 'to'

Solution 1:

"so as to" and "in order to" are equivalent. "In order to" is more common:

"in order to" shows a desired situation (achieving your goal) and an action that is done to get to that state (study) - "I study in order to achieve my goal"

Generally, this can be shorted to "to": "I study to achieve my goal". (However note that "to" has many other uses.)

Solution 2:

Speaking as an Englishman, and (supposed) fluent English speaker I would use the first syntax in normal conversation - the second seems to be too formal for everyday use. However, the decision is yours, as you are correct in that they have the same meaning.