Physics with Calculus
A lens changes direction only because of its color-dependent absorption, whereas a mirror changes direction because of transmission.
A lens and a mirror both operate by the same law, but one is drawn on the opposite side of the axis.
A lens works because light speeds up in glass and therefore always bends away from the normal, whereas a mirror slows light down.
A lens relies on refraction at boundaries with different refractive indices, whereas a mirror forms images by reflection.