"so that" denotes a result or logical consequence, and sometimes is equivalent to "in order that". The confusion of "so that" with "such that" may be a consequence of influence of the German language.

Take x to be a real number so that x^2 is non-negative. [Correct]

Take x to be a real number so that x^2+3 is greater than 4. [Incorrect]

Take x to be a positive real number such that x^2+3 is greater than 4. [Correct]