Tombs were a strong part of their culture. Egyptians believe that after death, the spirit could wander to foreign places that might make the souls lost to the point of no return. They believe that by building tombs, these souls always have some sort of place to guide them where they can always come back to. Practical Geometry is needed to built large sized tombs for the nobles.
On top of that, they rely on agriculture as their main source of income. Often times, rains might cause the river to flood and destroy the agricultural land near it. So they use geometry to built proper dams and developed an irrigation system to allocate the water to a land that located prerry far from the river.
