The drawing method of rotating a simple figure 90 degrees is to select one of the two lines drawn by a fixed point in the figure, rotate it 90 degrees clockwise/counterclockwise around the fixed point, and then supplement the incomplete part of the figure.

First of all, the nature of rotation

The rotation of a graph is the positional movement that each point on the graph rotates by a fixed angle around a fixed point on the plane; Wherein the distances from the corresponding points to the rotation center are equal; The size and shape of the figure have not changed before and after rotation, but the position and direction have changed, and the rotation center is the only fixed point; The angles formed by the connecting line between the two groups of corresponding points and the rotation center are equal, both of which are equal to the rotation angle.

For the problem that the graph rotates 90 degrees, we can also consider it this way: taking the vertex of the right angle as the rotation center, then the rotated right angle edge is perpendicular to the original right angle edge. When both right-angled sides find a vertical line segment, connect the third side to get the rotated right-angled triangle.

Second, painting skills

The principles of graphic rotation and graphic translation are basically the same. The shape and size of the object have not changed before and after rotation, and the corresponding points and corresponding line segments are equal, and the corresponding angles are unchanged. As long as you master this method, when you rotate, you only need to find the rotation angle, rotate point by point, and then connect the rotating points, and you can get the rotated figure.

Rotate the graph and the center of symmetry:

1, rotate the graph

In a plane, turning a figure around a point by an angle in a certain direction is called the rotation of the figure. This fixed point is called the center of rotation and the rotation angle is called the rotation angle.

The rotation of a graph means that each point on the graph moves around a fixed point on the plane at a fixed angle, in which the distance from the corresponding point to the rotation center is equal, the length of the corresponding line segment is equal to the size of the corresponding angle, and the rotation does not change the shape and size of the graph.

2. Center of symmetry

Rotate the graph around a point by a certain angle, and it is consistent with the original graph. This figure is called rotational symmetry figure, this fixed point is called rotational symmetry center and the rotation angle is called rotation angle. (The rotation angle is greater than 0 and less than 360)