Method: Fold the square paper in half along the center line, starting from the bottom of the crease, cut the diagonal first, then draw a semicircle or a large semicircle and cut it back to the fold line. When you open it, you will get the favor of the symmetry axis.

Extended data:

axial symmetric figure

There are many kinds of symmetrical figures, such as axisymmetric figures: if a figure is folded in half along a straight line and the two parts overlap completely, such figures are called axisymmetric figures.