Large pizza versus medium plus small without a ruler

One large pizza is priced the same as a medium and a small bought together. Each pizza is cut into six equal slices and comes in a square box, but you have no ruler or other measuring tool. How can you decide which choice gives more pizza?

Compare radii with Pythagoras. A slice's straight edge equals the pizza's radius. Lay a medium-slice edge and a small-slice edge along two sides of the box from a corner, forming a right angle; if a large-slice edge is longer than the hypotenuse joining their ends, then $R_L^2>R_M^2+R_S^2$ and the large has more area.