Yes. The square is a special form of the angle notation, which specifies a right angle. It is common to put it there, since it clearly defines that triangle as a right-angled and not just a very close one.
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As an example: a square has four right-angles, one in each corner, and they prove that a right angle doesn't always open to the right.
A square
a right angle has a square in the middle so the you should know has a 90 degrees
The square drawn in a right angle simply is to indicate that the angle is, indeed, 90 degrees.
Each angle in a square is 90 therefore each angle is a right angle.