Technically I dont know what mean "so as to" and how use it. thanks for explanation
So as to means in order to. He studied English night and day so as to get admission to Cambridge.
He had to use a ladder so as to reach the top of the wall
"So as to" expresses the purpose/objective/aim. Its negative form is: so as not to +stem.
Most of the time the full expression "so as to" should be reduced to "to." For example drop the "so as" in the previous examples above and leave only "to" and the meaning remains the same. In modern English writing, the less words used, the better.