One light ray from a fish dorsal fin-tip under-water (n=4/3) enters air at x=0 exactly along the Normal ; another light ray from the fin-tip enters air at x=0.1 [m] , at a 5.0° angle from the water surface Normal.
Snell will tell you where the light is really coming from, so you can use a trig triangle to determine how deep the fish really is.
follow-up: trace-back straight along the 5° line to make a "virtual right triangle" of how deep the fish appears to be; is the fish deeper or shallower than it appears to be? by what factor?
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