The slender mirror visually gives people the feeling of longitudinal stretching, while the wide mirror visually produces transverse stretching. More importantly, using the principle of optical refraction, the convex mirror with thin side and thick middle can reduce the lateral proportion of imaging, while the concave mirror with thin middle and thick upper and lower ends can lengthen the vertical direction of imaging, which can both produce slimming effect. It's just that the radian of these concave mirror is very small, which is not easy for the naked eye to detect.