When the adjacent angles formed by a straight line and another horizontal straight line are equal, each of these angles is called a right angle, and this straight line is called perpendicular to another straight line. In other words, an angle equal to 90 is called a right angle.

Extended data

An angle greater than 0 and less than 90 is called an acute angle, an angle greater than 90 and less than 180 is called an obtuse angle, and an angle equal to 90 is called a right angle. ?

Example 1: Among the following figures, the figure at right angles is ().

Analysis: A, isosceles triangle, two angles less than 90, namely two acute angles, 1 right angle. So it's not all right angles

B, it's a rectangle, and all four corners are 90, that is, they are all right angles.

C is a quadrilateral with 1 acute angle, 2 obtuse angles and only 1 right angle. So it's not all right angles

D is a pentagon with two acute angles, 1 obtuse angle and only two right angles, so it is not all right angles.

So the answer is B.